It's a bit tough to quantify. Ordered lists are too rigid for this question imo, specially since there's only going to be a couple of classes that we'll have a consensus on. The truth is that every class is extremely viable solo in this bracket, so I'll give you a list that is completely subjective and merely tells you what I would most want to play solo, with the goal being to win games efficiently.
Hunter >> Tracking, Viper Sting, Traps - if there isn't one on your team you'll regret it.
Druid >> Miracle FC, also pretty much the most crucial class to have on a team.
Mage >> Go Fire and put the fear of god into the EFC, insane CC, high skill cap.
Paladin >> Best heals, best support with BoF, incredible tanking.
Rogue >> Return flags, quick caps, but it's easy to have too many on the team stealthing around ineffectively.
Shaman >> Purge, great support, GW, obviously PoD WF is awesome, but Resto is also a really powerful spec for O.
Warrior >> Intercept means you can break defenses and your damage is outstanding, with support probably the best all around.
Warlock >> Most damage, owns mid but going deep O or D is generally inefficient so struggles to lock down objectives, slow.
Priest >> Extremely powerful, but needs good little minions that are worth supporting, slow.