ran out of space so heres carry on
the xbox 360 market place you get demos, gamer pictures, backgrounds, videos and add on's to games, the demos are free as are SOME backgrounds and gamer pictures but you have to pay for everything else and xbox live gold is $40 a year to run
the ps store is the same thing with demos, videos, backgrounds, ps1 games and game content, it cost nothing to run the account and it cost nothing for the demos, pictures and videos but you have to pay for the ps1 games and game content
both have pros and cons
the xbox 360 can run cds and dvds right out of the box but needs the HD-DVD add on to play HD-DVD's where as the ps3 can run cds, dvds and blu ray movies right out of the box without having to pay loads for add on's
my suggestion is look at the games on the systems now and look at upcoming games and get a systems based on that, now lets wait for theends beat down on the xbox 360