Uuuh, that's a hard question! Best game for it's asking price is Metroid Prime, since you get 3 games in 1. But as for length, I'd say Xenoblade, but if you want local co-op I'd say Mario Kart, Smash Bros or NSMBWii. My personal favorite might be Twilight Princess though...
All in all, Wii was a pretty great console!
I'm on Twitter @DanneSandin!
Furthermore, I think VGChartz should add a "Like"-button.