In my opinion there is no "best class" , it all depends on the persons playstyle, the point of a game is too have the classes balanced anyway, so when all choose one because it is slightly overpowered at some point ruins the balance.
And yes, Hunter is pretty good for soloing, but there are other classes that are good at it, nearly all I would say.
Priests? Yes they can solo, they have decent damage and can heal themselfs, when they get to AoE they just gather-kill-heal-kill-get the exp.
Warriors? Even though in the beginning they have to sit down and get there hp and mp full, when they turn into berserkers or paladins they become solo machines, especially paladins since they can heal themselfs and have a pretty decent mana pool.
Mages? Well I dont know much about them since I didn't try them out yet, but I would say that they must be pretty good in solo... kill-run-kill
Archers? Well yea, as I said they are decent, they have slows and stuns from the beginning and a nice damage to back them up, when played properly they can even solo bosses easily with all the CC they have.
That's just my opinion and the way I saw things up to now.