I had one of each class at 50 and two warriors. I started leveling the two warriors (one for Venthyr and one for Necrolords) but quickly got consumed with only playing my main (venthyr warrior). I've attempted leveling my priest, warlock, DK and druid but I get burnt out on the leveling very quickly. So they're all scattered between 51-57. Someday I'll finish them but I think I'll wait for flying.