The XMB is simple and clean... a pretty well-proven user-interface concept. I think you'd be hard pressed to find any data, either with console multi-owner polls or academic data regarding interface design, to state otherwise.
I think the PS3's interface is the best of all three, although I do very much like the mellow tunes while I'm *not* navigating my Wii's interface (i.e. I'm feeding the cat or somesuch, and not gaming). The thing is, I don't usually spend much time in the interface (which is why I like the simple XMB, probably)... I'm a gamer.
IMO, the channel thing the Wii uses is shoddy and slow compared to the XMB. Point-and-click... bleh. Heck I got a PC (okay, actually 8 PCs) for that. I want game ASAP when I turn my console on... not navigation. I'm still trying to figure out why people even liked the Wiimote before they added the decent motion sensing tech. It wasn't like Wii buyers lived in some wasteland where no one had ever seen a pointing device... obviously I will never understand, until some app really does a great job of using the motion controller.
Its the nunchuk that is so cool... and that's far and away my favorite part of the whole Wii setup. If the Wii controller was a analog nunchuk plus a D-pad nunchuk (for the other hand), rather than the clumsy pointing Wiimote, I think I would be much happier.
