Oh wow, this is like....a really hard question, indeed. If I went by game comparisons, Wario has the Wario Land games, which are pretty awesome, Wario World, which is rather short, and...I have to give some credit to Warioware for actually developing him. Also, his crawling animation in SSB4, what the zel XDD and he has the (sadly patched) vectoring glitch that was pretty amazing while it lasted.
Waluigi on the other hand, is just downright awesome in the sports games. He has spin abilities that make SMG spins look pretty slow, he can swim on air, and in the golf/soccer games he has my favorite animations. Aside from those though, he doesn't get much limelight, which is kinda weird...It's like the issue with Daisy not appearing in mainstream Mario games since appearing in Mario Party 3/Tennis on the N64.
I'll have to say Waluigi. Also LOL to the genie shoes comment XD