In my opinion, the two best PVP classes are Scoundrels/Operatives' healers and Shadows/Assassins' tanks. You cannot beat stealth and vanish in PVP. A stealth class can defend a node longer than any other class while waiting for help, and you can always vanish, heal and go back to the fight again.
Additionally, Scoundrels/Operatives' healers are the most mobile healers. Their unlimited under 30% health instant heal combined with the other HOTs and moving around columns make them very hard to kill.
Shadows/Assassins' tanks have lots of tools, including pull, knock back, sprint, 10 meter range, decent damage, and that new teleport ability among others.
I am writing this because I would love to play a Sage in PVP but I get so frustrated when I get killed so fast. I rarely die with my Scoundrel's healer. I think all classes are balanced for PVE but in PVP the two above-mentioned classes rule.