Depends what style of game you like. :)
If you want a support class, chose between the chanter or the cleric, personally i prefer the cleric because he have lots of healing skills and you can transform him in a killing-machine by chosing the PVP stigma tree, cloth set and lots of MBoost Manastones.
If you want a damage-dealer, you can make a Sorcerer ( lots of MBoost, but few HP), a Ranger or an Assassin.
The Templar have a lot of PDefense, but he`s PAtk it low, so you`ll survive often, but u`ll kill fewer enemys. Anyway he`s good for tanking, so u`ll be a needed player for every instances or rbs.
GL and regards to all Elyos! :P