Fun is subjective. If you want a class that's fun for you to play, this question is completely irrelevant.
For example, Cannon Artisans until the recent Paradigm Shift patch were almost completely unheard of; yet, my main was a Cannon Artisan and it was pretty damn good at what it did.
Point is, pick a class you enjoy, roll with it and stick to your guns.
However, if you're in it to be an elitest, then just go for a Stun/Mute Mage since they're practically invincible when played correctly, or a Cannon Bourgeois if you want to grief people in PvP Arenas.
As far as the best PvM class, hands down Duals Raiders. They can solo practically every boss of every Dungeon with the right set-up.
Good luck, I hope you pick something you enjoy. If you don't, you'll just get bored and quit again.