Current WR characters as of late 2017:

Malibu [edit: WR held by Ludwig now], Texas, Hawaii - Huey
Colorado - Goofy/Pete
Every other stage - Ludwig

PerfectTaste's recommendations for newer players:

Unless you're very good, like super good, with Ludwig, I'd advise:
Everglades, Malibu, Hawaii, Texas - Huey
DC, Oregon, Colorado - Goofy/Pete
Every other stage - Ludwig

PerfectTaste's advice for NTSC-U/PAL players without the means to unlock Huey:

Unless there's some new alternate strategies out there I'm unware of, if you don't have access to Huey, then:
Everglades, Hawaii, Texas - Dewey
Malibu - Goofy/Pete