Get it for the PC and get a xbox controller that is the best bet. I would shy away from getting it for the PS3 not for any performance reasons or that I'm biased towards xbox since I have one, but for the simple fact it seems to take forever for the PS3s to get DLCs that both xbox and PCs get. If you don't care about the DLCs that will inevitably come out and can wait several months, if not a year, for them to come out if they indeed do come out than just get it for PS3, but be forwarned that you will not have access to user-made mods for the PC and will likely have a long wait for DLCs for the PS3.
Yeah, mods are one thing, but Bethesda's DLC is 360 exclusive. Not 360
and PC exclusive. Dead Money for instance just came out for both the PS3 and the PC at the same time. Both after the 360's release. If waiting for DLC is
that big of an issue for you, then the 360 is really the only way to go. That is of course unless Bethesda announces that the DLC will not be timed for 360's Skyrim. History dictates otherwise, but still, we'll all have to wait and see.