Oh man, what to choose... I'm no doubt gonna forget about one I love. And I can't just list one!
Based on the stand's visual design, I'd have have to say Cream, Sethan, and Grateful Dead. I don't know what it is about Cream, but I love it's visual design, and the way it "eats" itself and it's stand user. Also props to whoever at Capcom designed his moveset for the old game, as well as just the way he moves. Sethan for looking so weird and creepy, fitting for such an unsettling user like Alessi. And Grateful Dead cause, seriously just look at that thing! Just looking at that thing, you know it's big trouble, and it certainly delivered with one of the most tense series of chapters in Part 5.
Ability-wise, I'd have to say Hanged Man, Bastet, Crazy Diamond, Sticky Fingers, Metallica, Stone Free, and Diver Down.
Hanged Man, cause killer reflections is an awesome idea. Bastet, cause I love magnetism powers. Crazy Diamond, because I love the fact that it can destroy as easily as it can heal, as well as using healing to cause bad things. Sticky Fingers, cause amazing utility and near limitless possibilities. Metallica and Diver Down, cause destroying someone from the inside and re-arranging their bodies is so sick and twisted. And Stone Free, for the same reasons as Sticky Fingers. Too much?
Mind you, I haven't started Part 7, so there may be cool stands I have yet to discover