Well if Mass Effect 2 is coming out on PS3 it will come with it's own advanatages and disadvantages. Being U3 engine it will probably look and perform worse in hectic scenes than 360 version. There will be no AA. Advantage is all on one disc,
Digital Foundry will do the comparison and make 360 fans feel a little smug though I think it's a very small price to pay for having access to yet another awesome game no longer exclusive to the 360.