I'm a fan of the PS3 because of its superior capabilities as a general home media hub and the fact that exclusives available to it better suit my personal taste. I actually just made this decision recently, after a good number of years of not buying any new games. That said, for your purposes, I think the Xbox 360 may be a better bet, for the following two reasons:
1) I don't particularly care about the online gaming aspect on home consoles, whereas that seems to be an area of concern for you. The Xbox 360's online experience is clearly more polished than the PS3's, even if it costs you more. That said, I can still see this going either way for you since the difference isn't that large anymore and there's the annual fee thing. Which is why most of the weight of my reasoning goes into the next point...
2) If a large part of the usage of this console is going to be the movement-focused dance games and whatnot, Kinect is a far better technology for this than the PlayStation Move. The PS Move is literally a carbon copy of the Wii Motion Plus, but Kinect went a different direction that actually lends itself better to a number of types of games, most notably dance-oriented ones. The camera analyzes your full body's profile, and dance games that actually look at how your whole body is moving are possible. The PS3/Wii approach just analyzes something you're holding in your hand, which isn't quite as immersive an experience for a dance game and simply can't do things like look at how your legs are moving. The PlayStation Move will be better for things like shooting games that have you aiming at the screen, but I get the feeling those aren't the kinds of games you want to use the movement system with.
EDIT: One more thing. I get the feeling you don't have very strong convictions about the exclusive games on the two platforms (unless you're willing to hunt down a first-gen PS3 for complete backwards compatibility, in which case, hey, you get to play all the old versions of Resident Evil and Silent Hill!). Most of the games released on both look (very slightly) better on the Xbox 360 despite its inferior hardware because of the fact developers tend to develop the games on that platform first and then halfheartedly port it over to the PS3. Why? Because it's easier to reuse code between the PC and Xbox 360 versions of the games if they're also releasing the game on the PC. This is more the case with older games than newer ones, since another minor part of the issue back then was simply that the Xbox 360's earlier release meant developers were already very familiar with that hardware at a time when they were just starting to learn the PS3's.