Matter of opinion, and Blizzard seems to have taken a Rock-Paper-Scissors approach in regard to class balance.
As in a Mage will own a Warrior that will own a Rogue that will own a Mage, etc. (exp, probably not accurate). At least for 1v1 stuff.
Although from personal experience, in a raiding group, NE priests can be devastating (heals + hiding), and rogues (any race) are very PvP popular.
W/ druids, tauren > NE solo, NE > tauren group (stun vs. hiding).
Solo we own Hunters (hibernate the pet, root the hunter, close distance as bear), mages (mana efficient heals, shifting frees up movement), and rogues (roots + fearie fire). But Shadow priests, shaman, warlocks, and paladins own us.
In groups, shifting = attention = death, unless it's into Cat to Prowl.
Multiple rogues take us down quick, as do warriors (they can break the roots somehow, don't quite know how). However using Thorns on the guards and other players lets you do massive DoT w/ noone knowing, and Ressurection helps (once).
Pretty much, stay in the background, buff and heal, sending out a moonfire once in awhile (starfall and wrath = big line pointing at you = death). Maybe faerie fire the rogues, root some people. Just don't attract attention to yourself.