Wii
Joking, it's amazing how profitable the Wii is for Nintendo! Insane.
On topic I'd say that PS3 probably has the highest losses up to date but has at least 4-5 years to recoup those losses by selling HW in developing countries such as latin markets and middle east etc, like in the case of PS2.
Second would be the original Xbox, I loved that thing, but it must have cost MS dearly. And there is no way to recoup those losses, but it could be argued that the entry of Xbox signalled the fact that MS was interested in the gaming market and was used as a foundation to build up it's userbase.
Third is obviously 360, however, it's likely to go into profits now. Pretty amazing if you think about the high HW failure rate early on in it's life cycle, that they've managed to salvage the loss made as a result, which was probably no small number.
Disconnect and self destruct, one bullet a time.
