A good Mundo jungler maxes what first?

yes, it's Q.

Q gives you way more jungle clear speed than W and E

i put 2 in w, then max q

When Mundo was a strong jungler S3 it was W max, but camps have more HP on one big target now. E max was the transition, because you could run attack speed Marks and Quints and kill stuff really quick. Now? I dunno. Probably Q, because it kills the big monsters pretty quick and is what you want maxed for team fights.