i'm a big fan of the XMB on the PS3, but to be honest i prefer the interface that the 360 uses. yeah, you can customize some aspects of the PS3's interface, but the menus on the PS3 are limited when it comes to loading lots of content in real time. i usually have to wait to see what's what. not to mention that while there are just as many ads as 360 in the PS3 marketplace, there are none in the menu that you spend all your time in (my xbox). xbox just puts the marketplace content first and foremost, rather than hidden in a menu that you have to sign into to access - which, honestly, i prefer, because i'd miss a lot of stuff if i wasn't able to just browse the spotlight channel like i can now.
it's even poorer on the PSP, where you're waiting for several seconds just for the names of what you're looking at to load on-screen.