Personally I like a half-orc wizard who casts mage armour on herself, uses arcane recovery to regain that spell slot and then walks into battle with Magic missile and Shield (deflect damage from the enemy barbarian and if you still have slots deal damage back that doesn't rely on being intelligent). Dump stats for this build are Intelligence, Charisma and Strength.

I'd be interested to hear your ideas for strong low-level wizards.

I'd want to be a Tortle, not a Half-Orc

That works. I personally prefer the half-orc, because the wizard will survive one more hit (ie one more round to blast your enemies) with relentless endurance, but I see the appeal of an AC 17 wizard who hopefully won't get hit at all.

I'd want a Tortle Wizard, for an all comers pvp challenge

16str 12dex 13con 16int 10wis 8cha

Cantrip: Fire Bolt - reliable ranged

Natural Weapon - reliable melee

Have a Familiar, and then also Absorb Elements, Magic Missile, Shield and Tasha's Caustic Brew.

Though at lv 1, I think it will be a tough fight vs a martial class, I think this maximises chances though

Absorb elements is extremely useful. I think the beauty of Magic Missile is that at low levels it has a solid chance of one-shot kills against most enemies who can succeed on Str and Dex saves.

I think it's going to be pretty hard to beat a 1st level Tortle wizard.

for anyone except elf and warforged, sleep and manacle combination is hard to beat.

Shield + Shell = AC 23, if they can hit that at 1st level, that's pretty impressive. Then Sleep, remove their weapon and manacle them, Hit them with 2 handed quarterstaff with critical since they are unconscious. Move back 30 feet, if the hit doesn't kill them, they will need to break dc 20 str and half move to get up with no weapon, then you can sleep them again if you haven't used your shield spell or just move further back and take pot shots with firebolt.

for Elves and Warforged. Chromatic Orb for low Ac opponents or Hideous Laughter for High AC (with remove weapons and manacles)

You can't afford to dump Intelligence.

You prepare the list of wizard spells that are available for you to cast. To do so, choose a number of wizard spells from your spellbook equal to your Intelligence modifier + your wizard level (minimum of one spell). 

So to have 3 spells available, you need at least 14 Int.

Either way, a wizard is going to struggle hard in this. Not impossible, but a something like a beefy fighter definitely has the advantage.

Good point. But it isn't as essential to get that Int 16 if you choose to go with spells that don't require Int saves or attack rolls. Which means you can boost HP a bit.

I would have thought Monk was the best for this, because they get two attacks at level one and a high dexterity in order to go first

Monk is definitely solid, but fighter seems better. Fighter can dual wield short swords for the same damage output as a monk, but brings more HP,  more AC, and Second Wind for an even greater boost.

I think something like a Goliath Fighter is gonna be really tough for the wizard to burn through. They have 29 effective HP, 16 AC, and only have to tear through at most 9HP and 17 AC from a Tortle wizard.

How about Crossbow Expert Human Fighter?

Crossbow expert is great for maximizing your damage, but you lose out on some survivability. The wizard can survive your first turn with Shield or certain racial traits like Relentless Endurance, then kill you with an average damage Chromatic Orb. 

If we want to maximize the chance to win, I think the Fighter needs some defensive tools to ensure he can't be one-shot, which in turn lets him use second wind for even more HP. Meanwhile, his damage is already high enough to one-round a wizard. Crossbow expert just makes that damage slightly more reliable.

I like this idea too. AC 18 would be hard to hit and bonus action healing to regain 1d4+5 HP should tide them over. And I am changing the title of the thread to Strongest 1st Level Character (In a One-Shot).

If this one shot is taking place in a forest or any place they can use their natural hide ability go with a wood elf archer.  You have to see them to hit them.

With their action? And they reveal themselves when they take a shot.

 Though to be fair, you'd get advantage when you do shoot, next turn

Quote from Stephanie252 >>

With their action? And they reveal themselves when they take a shot.

Yes, but you still have to beat your opponent's perception check.

Hunter's Mark and Go invisible. Then shoot at advantage and again with like crossbow expert (to make sense of the free second bonus action). Could work. Oh, I'm not saying it is fantastic, there are better options.

It could. But when you go invisible, it doesn't hide you (an how do you plan to go invisible at 1st level again?). That still takes an action every turn if you reveal yourself (by trying to actually hit your opponent).

I am liking this war cleric build:

With 2 attacks at an average of 10 damage each, your can pretty reliably one-round most opponents. With 11 HP and Stone's Endurance, you can pretty reliably survive any turn from an enemy. 

Sanctuary is a strong bonus action option against beefier opponents that can survive your onslaught. You deliver one powerful attack, and if it doesn't look likely that your bonus action attack will kill them, you cast sanctuary. Most other classes will have <50% chance of saving against it.

Guiding bolt gives a ranged nuke against squishy targets that try to kite.

I think the odds are very high if they win initiative, and still pretty decent if they lose initiative.

It might be worthwhile to swap to longsword + shield and use Shield of Faith for 20 AC, but I'd have to see what builds threaten this before making that call.