I'm undecided between Voldemort and Snape, though Voldemort and Dumbledore I have no clue about as I don't remember reading and distinct potions they have made, maybe except for the ones Xandico pointed out for Dumbledore.
I think Lily was more like Hermione, as in she was more 'By the book' whereas Snape was an inventor, he practically found out new ways to make potions, so I'd say Snape was better than those two.......Of course he's had more practice, but heck, practice makes perfect.