If you're talking about video and proper media archiving neither the Xbox OR the PS3 have anything like sufficient capacity - the xbox's 20/60/120/250 gb is woeful, and even the PS3 can only be upgraded to something like 750Gb - largest 2.5" drive available.
For media - in my opinion, the only sensible, future-proof and truly flexible way of doing things is with upgradeable centralised storage, after that, the 360 and Xbox are pretty much equivalent.