Or the bestest familiar?

You decide!

We all know that the King of the Roost used to be the overpowered owl but now that we've been exposed to the tauntingly delicious delights of the hellaciously hot abyssal chicken, we all should acknowledge not only its greatness, but also the indisputable fact that it would more than likely devour the owl in a flurry of blood and feathers and, moreover, that this is, undoubtedly, a good thing (and also hilarious to witness).

Now, I'm not going to get into some boring stat-for-stat tit-tat (even though we all know that the abyssal chicken would win) because if that is your primary concern, then stop being a wizard and get your warlock pact of the chain going and get yourself an imp, you power hungry mega-munchkin, you (not that this is a bad thing). What I will do, however, is exposit the virtues of roleplaying your very own familiar as a quirky, albeit terrifying, addition to your PC family. Sure, it might nibble on the extremities of your friends while they sleep, 'causing them to scream in pain whilst in the middle of a dark forest or deep dungeon, but like the rogue who steals the party loot, we should not judge the abyssal chicken for who it is, at its core, but instead for what it can bring to the table in terms of utility and ability. And when it comes to the usefulness of an abyssal chicken, I highly doubt there is anyone left (alive) who will question its application and resourcefulness; it does, after all, thrive in an exceedingly hostile environment. So we won't even acknowledge any dissent here and must simply accept that an abyssal chicken provides far more value to a party than does a mere mundane familiar of the beast variety.

What we have here, fellow adventurers, is a magnificent opportunity to expound upon and highlight the brilliance of a familiar so exceptional that it conquers transplanar boundaries and brings delight and festive welcome to all whom behold it. It also tastes delicious with mint-gravy.

VIVE LA ABYSSAL CHICKEN!*



*Until we get hungry.

Give me winged angry cat tressym all the way.

That chicken looks finger lickin' good.

this is my new familiar for life  unless another fits better but thats besides the point I need this IRL it could eat my enemies 

According to all the RAW printed text, Crawfords twitter posts and sage advise articles: TL;DR: Abyssal chicken #1 Familiar confirmed

You gain the service of a familiar, a spirit that takes an animal form you choose: bat, cat, crab, frog (toad), hawk. lizard, octopus, owl, poisonous snake, fish (quipper), rat, raven, sea horse, spider, or weasel. Appearing in an unoccupied space within range, the familiar has the statistics of the chosen form, though it is a celestial, fey or fiend (your choice) instead of a beast.

• Variants in MM are for NPC's only, as stated by Crawford via Twitter. ONLY Pact of Chain Warlock may select Imp, Quasit, Sprite or Pseudodragon
• 13 HP Gazers, are NOT listed in spell OR Pact of chain & CANT be used by a PC (I'd optionally allow on Pact of Chain Great Old One Patron Warlocks)
• In combat, it rolls its own initiative. A familiar can't attack, but it can take other actions as normal. (A Pact of Chain familiar may attack) 
• Caster CAN sense what it senses while within 100 ft, A familiar CAN Deliver touch spells
• Can be Dismissed/brought back as an action, CAN be resummoned, possibly as a different animal
• Below lists the "other" usable by Player Character casters that arnt also "pact of chain" warlocks
• As in BOTH the Almiraj's & Flying Monkey's descriptions:

• "[..] the find familiar spell can summon a [..]" "Almiraj" (or) "Flying Monkey" (respectfully).

• As in Tressym's description: 

• "A person who casts the find familiar spell can choose to conjure a tressym instead of a normal cat."

•  As in Abyssal Chicken's description:

• "A character who casts the find familiar spell can henceforth choose to conjure an abyssal chicken instead of a raven."

• This makes the abyssal chicken #1 RAW allowed, for all non-pact of the chain spell casters. This is due to its HP, AC & its various resistances/abilities. It still cant attack, but it can soak damage as a blocker + deliver touch attacks in flight. Make it wear Breast plate or Half plate barding for AC 16, or AC 17 respectfully, with 10HP to boot! 
  * Pact of the Chain Warlocks should almost always choose the Imp, its better in many ways & an Imp in Breast or Half plate barding is VERY deadly!
• The options with most HP, hi to low:
  10HP Abyssal Chicken/Imp > 7HP Pesudodragon/Quasit > 5HP Tressym > 3HP Almiraj/Flying Monkey/Octopus > 2HP Cat/Crab/Lizard/Poisonous Snake/Sprite > others 1HP

A "typical" familiar can't attack, without your using Dragon's Breath spell on it, so "Damage Soaking" is King!

Quote from aazard >>

• If a Pact of Chain Warlock's pact given familiar dies or decides to leave its master it CAN NOT be resummoned 
• Below lists the "other" usable by Player Character casters that arnt also "pact of chain" warlocks
• As in BOTH the Almiraj's & Flying Monkey's descriptions:

• "[..] the find familiar spell can summon a [..]""Almiraj" (or) "Flying Monkey" (respectfully).

• As in Tressym's description: 

• "A person who casts the find familiar spell can choose to conjure a tressym instead of a normal cat."

•  As in Abyssal Chicken's description:

• "A character who casts the find familiar spell can henceforth choose to conjure an abyssal chicken instead of a raven."

• This makes the abyssal chicken #1 RAW allowed, for all non-pact of the chain spell casters. This is due to its HP, AC & its various resistances/abilities. It still cant attack, but it can soak damage as a blocker + deliver touch attacks in flight. Make it wear Breast plate or Half plate barding for AC 16, or AC 17 respectfully, with 10HP to boot!

A familiar can't attack.. so "Damage Soaking" is king!

 Pact of the chain can resummon their familiars if they die, where does it say they can't? Also pact of the chain still uses the find familiar spell, so would have access to all these additional familiars as well. The abyssal chicken's flight is mostly inconsequential since they can't stay airborne. 10 HP starts getting 1 shotted pretty early in campaign (just not as early as 1 HP).

I also added links to all the monsters you referenced.

,if u have any suggestions I'm trying to improve my formatting so everything pony references stuff on D&D Beyond

See here for the links to sage advice and Crawfords twitter answers, it has good info, but your right for the pact of chain they can be resummoned (its non pact of chain warlock npc's with odd familiars that cant RAW). 

PS it might only fly 30ft for a turn but it can dash & still deliver a touch attack, for you, as a bonus action before it loses flight that turn.

10HP,  but its resistant to cold, fire, lightning plus immune to blinded, poison & poisoned 

Drop a Heroism on the Abyssal Chicken, up to 5 temp HP at the start of each of its turns plus immune to being frightened, maybe other "buff's" to add to its AC, give it temp HP and/or that might cause its attackers damage. Once you get the Dragon's Breath spell, this little guy gets an action it can use, thats not an attack, so familiar can use it, with its action, to do damage. A small grab of Magic Initiate for the cleric cantrips "resistance" & "word of radiance" (or guidance) along with "heroism" can really make a familiar (or you) tankier.

All Buffed up it might have 10HP (15HP if DM allows max roll) & 5+ temp HP a turn, AC 17, take half damage from fire/cold/lightning, be immune to blindness, poison/poisoned frightened Plus able to do 3d6+ per turn with its own action (if you have Dragon's Breath spell) 

It should be able to tank a Bugbear, Hobgoblin or a few CR1 goons every turn, eventually tossing out a "15ft cone", of avg 10 damage, each turn also

But hunting down a Gazer or Pesudodragon is the ultimate I think, if you can "tame" (bribe with rats?) one. I cant see a non pact of chain warlock getting a demon, devil and/or "true" Fey as a familiar in most campaigns. But a Hexadin riding a Peryton "greater steed" & a pact Imp familiar, yes please.

I prefer the power of a CHICKEN FROM SATURN!

(As you might have noticed, my location is Northeast Saturn, and the spiecies of Saturn Chicken is most common there!!!)

Abyssal chickens are the best familiars.

I looove Flumph Familiars, and while the Abyssal Chicken is cute, I'm always gonna go a tiny owl or a ginger cat, because I adore Frumpkin.

EEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE

An Abyssal Chicken is the Best Familiar Dinner. (It's precooked.)

Quote from 7BitBrian>>

People often forget a few major things when they discuss barding, whether for Mounts or Familiars.

No mounts nor familiars have any proficiency in any sort of armors. So by equipping them with any sort of barding you are giving them disadvantage on any ability checks and attacks that rely on Str or Dex(this means any and all skills that use Str or Dex as well). So no matter if the armor itself gives disadvantage or not, all familiars and mounts automatically have disadvantage on all stealth checks if they are wearing barding. Same for athletics checks if they are trying to lift or pull something. And depending on the barding the mount/familiar may not have the Str to use it and will have reduced speed because of this.

(You I believe in this context refers to the DM.)

If your DM says that your mount/familar isn't proficient in armor that is specifically designed to "protect an animal’s head, neck, chest, and body" and is literally from the section called "Mounts and Vehicles" then they probably just don't want you using a mount/familiar during combat in general and should say as such.

AS for mounts, the Strength requirement is a concern for Heavy barding, however several mounts have a STR high enough to use even plate armor. Besides most people don't ride their armored mounts into stealth, but if you do decide to do so, disadvantage on stealth is a valid concern. It's the price you pay for bringing any heavy armored creature to a stealth mission.

As for familiars, yeah probably give them medium armor, and yes you would have to specially get barding designed for familiars, but that I assume applies to all mounts as well (which is probably one of the reasons barding costs so much).

Edit: Some other notes, yeah I know you address the STR requirement in a accurate manner, but I thought to reiterate it just in case. Also, another thing worth noting is if most familiars have a high enough STR to be able to even carry barding considering it weighs double the amount of normal armor. Although your DM may rule otherwise (in terms of weight) since it's armor for a tiny creature not armor for a massive war elephant or something.

Yeah I can see a good argument as to why a familiar wouldn't be proficient in armor, but I could also see a good argument the other way around.

Edit: That being the barding is (presumably) designed specifically for the creature in mind, but at the same time yeah I can see why you might say a familiar who is mostly just a scout isn't used to the feeling and weight of metal on them no matter how fitted it is.