I don't really care which one is doing better to be honest. I like that the ps3 has free online. I like the halo series so far on the 360, but recently my xbox 360 year subscription expired. I haven't played ODST, but heard the single player wasn't long and that the multiplayer is halo 3 mp. But I will end up buying a subscription later on for it, if its worth the money for gaming online.
The only time I have paid, is for more mp levels on halo 2. I bought that one expansion disk. Still don't really care to pay extra for content that doesn't effect the quality or in this game perhaps quantity. I love mass effect 2 though, its one of the best game's Ive played that has a lengthy single player. Still Like how long oblivion is :)... and fallout 3 is pretty good even though I haven't got into that game that much.