Obviously it depends on the character. I've given it the most thought as Bowser (though I don't really main anyone) and with Bowser I almost always go for Smashville, and probably would even if I didn't usually stick to relatively neutral stages. Smashville is great for Bowser - its small size and moving platform make it much easier for him to overcome campers than on a stage like, say, FD. It also makes recovery less of an advantage and powerful blows more of one (since you don't have to go very far to recover or get KO'd) - thereby downplaying one of Bowser's weaknesses and emphasizing one of his strengths. The relative lack of platforms makes it much easier for Bowser to keep the game pretty grounded, which is where Bowser really excels (the one platform is enough to help with camping but not to make it a very "aerial" stage).
To summarize, a small, straightforward stage that lends itself well to grounded game play but not to camping is exactly what Bowser wants, and that is exactly what Smashville is. They should probably rename it Bowserville.
Oh, as a sidenote, Bowserciding from the moving platform while it's not over the stage is easier than Bowserciding from the actual stage, so that's another advantage.