Best Caster?

[Talamare]

You're a Wizard? Well, you can prepare another spell another day, but that's a few pages of your book you'll probably never read again. You can just hope that your DM will throw a few bones (read: spells as loot/trade) at you soon.

You find that particular spell potentially great, but you are afraid you'll never see a chance to really use it (like Water Breathing)? For every class except Cleric and Druid, you have a tough choice to make because it's taking one precious "spell known" slot for a while, confer above.

Druid is the only one that can really use all the spells, even the most niche, because you don't care about reducing your "always useful" spell list by one-two "slots" if it's only for a day.

What exactly are you talking about?
You don't lose the Spell from your Spellbook when you prepare a different set of spells.
You can ALWAYS go back to it the next day.

Wizards can prepare Wizard Level + Int Mod spells
Druid can prepare Druid Level + Wis Mod spells

both classes effectively learn every spell from their list.

What sort of hostile DM that actively attempts to screw the player are you playing with that would lead to the sentence "DM throws you a few bones"

[Witty Username]

By Power?
-Wizard
-Sorcerer
-Druid
-Warlock
-Bard
-Cleric

By Personal preferences?
-Wizard
-Warlock
-Bard
-Druid
-Cleric
-Sorcerer

I very much like directly motivated characters, wizard and warlock do the best with this idea. Casters that choose to be spellcasters and have a goal and purpose pursuing magic is appealing to me, and helps me make cohesive characters. The next is gameplay, I like playing the utility support types and having flexibility to get very specific on themes, Warlock, Wizard, and Bard all do this very well which the widest arrays of choices for casters. Cleric would be on this list too, but I find the base spell list of the class very restrictive which makes roleplay for some of the domains difficult. Druid is a bit of a special case, as I have had an affection for the class since Ad&d and while I can't tend to fit it with a variety of concepts, it tends to be evocative enough in its focus. In short, I don't always want to play a hermit type that wields the forces of nature, but when I do, I play a Druid.

Sorcerer is the least appealing of the casters for me, as I find the themes for the a strange combination of shackling and unhelpful. The angle of inherited magic makes characters feel disjointed and the abilities of the sorcerer tend towards the generic so it doesn't carry the specific bloodlines very well. I tend to gravitate towards warlocks and wizards when I have a concept that suggests sorcerer. Its pretty powerful though, especially if using the Xanathar's or Tasha's subclasses but it is deadly enough with a warlock or paladin multi-class. I tend to use it when I need a feature from it that I can't get elsewhere.

And for those that have noticed it on my list, No hate towards anyone that likes clerics, I think they are the weakest full caster, but that is not saying much (kinda like saying the weakest ICBM). And they are primarily as low as they are because of the frustrations working with the base class list for specific themes. I find full casters fun, including cleric and sorcerer, in fundamental ways and will still play them from time to time as the mood strikes me.