For me, I tend to like most spellcasters, especially spontaneous ones. Part of it might be because all the spell management is a lot to keep track of, especially at higher levels, even if they give more flexibility. I love Bards a ton. Spellcasting through performance is such a cool idea. Not to mention the range of flexibility they offer while still being spontaneous casters, since spells aren't their sole purpose.
Sorcerers are also awesome, both because of the "simpler wizard" model of spellcasting (I know I'm oversimplifying), and because bloodlines are so cool for flavor and roleplaying.
For non-spellcasters, I'd have to say probably Rogue, due to the sneakiness, and the skill flexibility. I still like when I'm able to have some spells, so Arcane Tricksters are more so my type of Rogue.
So final verdict for favorite, probably Bard, Sorcerer, and Rogue, in no particular order.