Answering to first post:
Vice City has the better overall storyline atmosphere. But once you beat the game, there is not much to do except boost your pilot ranking and criminal rating etc. Although this is my favorite GTA for some reason.
Vice City Stories has a great storyline, but not quite as good. Though, the missions are more challenging than VC. I love the empire building feature and swimming, more combat moves, phil collins, more planes and helicopters and the slightly better soundtrack make VCS soundtrack even more amazing!
These games are both great!
The main difference from VC to VCS is the game's engine and more features like swimming, cycling, more interors, the buildings light up and look very nice, etc.