I'd say the decision of which console to buy depends on a couple things:
-- are you interested in the exclusives that a particular platform offers?
-- do you have a lot of friends who own a particular platform and who you want to play online with?
I personally don't play online much, so I went with the PS3 because it has a lot of great exclusive games. As number1laing notes, one of those exclusives is a high-regarded baseball simulator, which might be sufficient reason for you. There are various lists online of the best games exclusive to each platform; take a look at those, read some reviews, and see if they interest you.