I've been going 360 so far, since it was my first console this gen and has kind of become my default setting. Plus the DLC for things like GTA IV and Fallout 3 make the 360 versions for those a no-brainer.
But if I find myself playing my PS3 more, which is quite possible now that Sony have realized that games > whatever multimedia hub bullshit and have really begun to bring it in terms of exclusive games, then there's a better chance I'll start to get PS3 versions. Or if they give a compelling reason to choose their version - say, some kind of connectivity between FFXIII and Versus.
For BioShock in particular, I don't think the challenge rooms (which you have to buy separately, right?) and marginally better graphics of the PS3 version make up for being twice the price.
