The main functionality I want from a console UI is fast access to my library of games and media.
In that regard, the PS3 trumps all. The simple grouping of games under PS3/PS2/PS1/Minis/NeoGeo and listing them in recently played order means the games I want are literally a button press or two away. Accessing the store is quick (even if the store UI has a lot of issues)
The Wii is in second place, only trailing the PS3 due to the sluggishness of accessing games hidden in the SD Channel. Again, access to the store is fast.
Rank last is the 360's abomination. It only exists to show you ads and shove the Live branding down your throat at every opportunity. I hate it, and its gotten worse with each redesign. So many button presses required to do anything. Finding games in the store is a chore. Horrible.
For handhelds, there's not much between the Vita and 3DS. Both work well for the most part. The Vita is fine, especially now you can use both controls and touchscreen. I'm not a fan of the odd number of bubble per screen, and it desperately need folders.
The 3DS has improved greatly with folders, but it still has an inconstancy with what screens let you use controls and some that force you to use touch. But as for fast access to game, it works perfectly.