Fox gets -3'd by ICs, Pikachu and Sheilda, and also has a really tough time with Diddy apparently. On top of that, he doesn't really go even with anyone in top tier outside of Falco (who should be less common since he also gets beaten fairly hard by ICs and Pikachu) and MK I suppose.
Wolf gets -3'd by Pikachu (I suppose this could be -2), Wario and DDD, while apparently going even with ICs, Oli and Marth.
ROB gets -3'd by DDD and ZSS, and also has a pretty tough time against MK and Falco (no I don't think MK is a -3 for ROB) and apparently Olimar (I don't agree with this either, seems like -1). He goes even (or possibly beats) ICs, and also goes evenish with Marth and Pikachu.
I suppose realistically you could make a case for Wolf > ROB cause his counters (Pikachu, Wario, DDD) aren't that common, and he has more even top-tier MUs than ROB, but I think theoretically ROB is better because I think Pikachu and Wario should have more rep, but they don't.
It's also a matter of personal bias.