Ultimately it boils down to not which system is better, but which games are better. Too many people make the mistake of buying the most powerful system and only later realising that it doesn't actually have many games they like.
For example I could have bought Soul Calibur for my PS2 or GameCube - in the end I chose PS2 because the gamepad is very important to me. The Cube may have the prettier graphics, but what would be the point if the controller ruined my gaming experience.
As for XBox, I know a lot of people have problems with the pad, but I can't really comment myself. If the only reason to get an XBox is for FPS's then even that seems not a good reason. Whilst out of the consoles the XBox may offer the best FPS's (although I'm sure Metroid Prime might have something to say!), all of them pale in comparison to PC FPS's purely because of the control mechanism.
Mu advice would be to first understand what games your bro would like to play - and then choose the system that has the most and best examples of those game-types.
Play Games... Not Systems...
- S
__________________
|