Honestly, they're all lacking diversity in the quality titles they provide ...
I would say that the Wii has a slight edge in diversity at the expense of depth in a lot of genres; this is mainly caused by the diversity that Nintendo brings to the library alone ... Super Mario Galaxy, The Legend of Zelda, Super Smash Bros, Super Paper Mario, Metroid Prime 3, Mario Strikers Charged, Fire Emblem, Battalion Wars, and Mario Kart are all games which are all very good games in different genres.
Basically, if you eliminate Shooters, Sports games and racing games the HD console's line-up becomes pretty sparse; in contrast you can't really decimate the Wii's line-up with the removal of a couple of genres, but they probably only have a couple of good games in each genre.
