Note: Only classes that go up to 9th level spells are on the list.

My vote is on Cleric, they have some of the most powerful spells in the game AND can bring people back from the dead. Let alone the things they can do outside of their spells, though I might be Baised I like them an awful lot.~

These questions never really sit well with me. Best for what? The different classes have their different strengths and weaknesses. If you get answers, they'll be answering what their favourite class is, rather than what is best.

Best for general play, how good the class is overall and how well they can help the party.

Wizard; no limit to number of spells known, largest spell list of full casters, greatest range of versatility, can cast the most spells in a day (as long as it's a ritual and in their book they can cast it without expending a spell slot), can learn additional spells any time not just at level up (as long as the gold and downtime hold up), plus always considered the smartest/wisest in the room (even when patently untrue). 

Wizard gets basically all the best spells, sans the resurrection ones. They can potentially learn ALL of the spells on their list and they can switch their spells each day.

I prefer cleric, but we all know the wizards get WotC's favoritism.

If you had said up to 8th spell level, it's Cleric.

As soon as you throw in 9th?  It's Wizard.  Being able to have every spell in your book, cast them as rituals if they qualify AND have on demand access to every single spell in the game at 8th or lower via Wish while ignoring costly material components?

It's not an argument.

Clerics are better at levels 1-4, but overall I have to give it to Wizards. They just have too much going for them, having just about every good spell, besides the ones that are Cleric exclusive. Unfortunately, Wizards have more good spells than Clerics do, so once weapons and armor become less relevant, so do Clerics in comparison to Wizards. (I still think Clerics are 3rd best, behind Paladins).

Quote from Lycaon1765p >>

Wizard gets basically all the best spells, sans the resurrection ones. They can potentially learn ALL of the spells on their list and they can switch their spells each day.

I prefer cleric, but we all know the wizards get WotC's favoritism.

 Actually Clerics get this without having to pay a fortune to copy them into their spellbook!

Any 17th level Wizard can raise you from the dead, it's called Wish.

Wizards have better spells in general, in particular for Combat.  Also, their limits are monetary and time.   Whenever you have to screw over people outside of the normal methods, that means that class has more power using the normal methods.

Compare at say Level 3rd spells

Best Wizard:  Fly, Counterspell, Dispel Magic, Hypnotic, Fireball, Slow, Haste. 

Best NON-Wizard spells: Mass Healing Word, Revivify, Spirit Guardians

Note, I excluded the Chono and Grav Wizard spells from either list

It is clear that Clerics do better outside of combat, while Wizards do better in combat.

Quote from Farling >>

Quote from Lycaon1765p >>

Wizard gets basically all the best spells, sans the resurrection ones. They can potentially learn ALL of the spells on their list and they can switch their spells each day.

I prefer cleric, but we all know the wizards get WotC's favoritism.

 Actually Clerics get this without having to pay a fortune to copy them into their spellbook!

 yes, but when you factor in rituals suddenly that spell book pays for itself. Remember clerics still have to have that ritual prepared for the day; wizards just have to "check their notes."

Wizard is my favorite class, and while I think they are the best too, I am biased. For me, the most important spell mechanic is Wish-Simulacrum combo, and to a lesser extent True Polymorph. The former lets you build an army of yourself, while the latter diversifies your army further. While wizards can abuse those to combos the best in my opinion, they are not the only ones who can abuse it.

Wizards are not really that special until they reach level 18 to allow their Simulacra spam level 1 and 2 spells, level 20 to allow their Simulacra to semi spam level 3 signature spells, and then they get another massive bump at level "21" and "22" with Boon of High Magic and Spell Recall.

Bards can also run the Wish-Simulacrum engine like wizards at level 17, get similar massive bumps at level 21 and 22, and have access to True Polymorph, but their simulacra cannot regain or spam spells in anyway. Sorcerers have access to the Wish-Simulacrum engine, the two Epic Boons, and can "regain" any 5th level spell slot and below via Sorcery Points, but lack True Polymorph to diversify their army. Genie warlocks have access Wish-Simulacrum, True Polymorph, regain 6th level and higher "spell slots" via Mystic Arcanum, but lack access to Boon of High Magic.

Clerics are great because you have full spellcasting AND heavy armor/martial weapons.  This makes you an incredably versatile adventurer.  As a cleric, it's easy to be a "jack-of-all-trades, master-of-none" player, because it's easy to change your playstyle day after day.  The ability to swap out spells each adventuring day saves you the stress of choosing spells carefully.  You don't need to worry about your spell selection during session zero, because you can always adjust it if you need to.  This reduces problems like learning a spell that seems good on paper, only to find out that it's almost never useful (at least in the campaign you are playing in).  Their spell list is very well-rounded.  While clerics don't get much of the powerhouse "blaster spells" of wizards or sorcerers, they get healing spells and can rush into melee if the situations demand it.  Clerics are helpful in a party with very few people, because the role of a tank, blaster, striker, support, or healer all comes just as easily for a cleric.  The key benefit is getting full spellcasting progression with heavy armor and martial weapons.  Your spells further augment your role of a melee-caster (spiritual weapon, spirit guardians, holy weapon, shield of faith). 

They might also be one of easier spellcasters to play, for several reasons.  One:  you don't have to stress about what spells you choose during character creation.  Two:  you don't have a lot of complex abilities to juggle at once, most domain features are pretty straightforward.  Three:  you don't feel "locked" into one particular party role, you can play all of them, depending on what is needed at the moment.     

There is no "best" class.

There is no "best" subclass.

There is no "best" race.

There is no "best" way to play the game.

There is only what each individual enjoys most, and that is a matter of individual opinion. Just let people play what they enjoy. Why does everything have to turn into a competition? 

Wizard. It’s just broken, even with no real features other than spellcasting. It’s not my favorite flavor-wise, though. The warlock takes that spot.

Wizards. They may be a bit weak at lower levels, but once they level up they can set a battlefield ablaze, and actually have spell slots to spare, unlike some other classes. Spells are pretty much their only focus. Besides, they are my favourite class by far.

Personally, I like Warlock. I think that there is no one best, there is someone who is personally better for you

They're called Wizards of the Coast for a reason...   I prefer Clerics honestly, but I guess Clerics of the Coast wouldn't roll of the tongue as well anyway :)

Yes, but it's kind of fun arguing over it! My favourites are sorcerers, and I know they don't get limitless spells, but especially WildMagic is always fun to see. They also get Metamagic, which is more  useful than some features wizards get!

I chose wizard but  between  cleric and  wizard it is  a very hard choice