Sholazar = best zone in Northrend, if not the game.
Nagrand = probably best zone in Outland, even though I'm a bigger fan of Zangarmarsh. Nagrand is still top tier.
Silverpine = decent zone. I never quested in it post-Cata, but pre-Cata it wasn't anything remarkable.
Duskwood = better in post-Cata, but still good in pre-Cata. Really, really fun zone back in Vanilla. I had lots of fun times questing there.
--
ziggie ziggie wop wop