I liked VC more.
VCS adds a lot of stuff to do after finishing the game. In VC you don't get to do much stuff after completing the game, but It still is my favorite GTA.
Although VCS had a graphical improvement, It was still dissapointing. The storyline wasn't as good as the original VC, and it had few missions. I would have forgiven that, but they were too damn easy, specially after you get the minigun. But the game was cheap, and fun for a while. Also I always hated that you start on the Little Havana island, instead of the Washington Beach island.