As a gish addict, I'm going to say Sorcerer. I love being able to attack and cast in the same turn with Quickened Spell, I normally take a Fighter or Paladin dip for defences and armour proficiency. This is just personal preference, it suits my preferred playstyle best.
I think the least well designed class is Warlock. The best part of the class is Eldritch Blast, which scales based on character level. Agonising Blast at 2, Pact of the Chain at 3, ASI at 4 are all things that Warlock gives that are useful as they are throughout the levels and the rest of Warlock isn't worth it compared to, say, Bard or Sorcerer. Unless you're going Bladelock but even that needs a Fighter dip to be even somwehat optimal.