Most likely Pro 64 bit, looking over the features list, there really is nothing a regular home user, even an enthusiast, could possibly need in ultimate, with the possible except (and this is stretching) of the hardware bitlocker security feature. I mean i guess if you were an ultra l33t h4x0r, that might be a feature that would be nice in case the feds ever raid you, but for us non hacker types, i can't see how using that would be anything more than extreme paranoia.