Have you played any game with a class-system? The choice is yours but I'll try to help you find out. If you like support gamelay, you should think about the warlock. IMO the hunter can also be a support because of the sniper. The titan is mainly a tank because of it's super, [i]Fist of Havok[/i], and the large armor ration((?) I don't know if this exists). A warlock can deal a lot of damage with the [u]Nova Bomb[/u], something like an agressive attitude, but [u]Radiance[/u]can also deal a lot of damage to a larger amount of enemies, but not kill them, as seen in the trailer called [i]out here in the wild[/i]. This may be used as support as I said before. The hunter is almost the most important piece of the fireteam. Taking enemies down with the sniper before jumping into battle and use the abilities to end with the battle with the help of a great support and the protection of the tank (the titan can use some kind of bubble shield for this). This is my opinion on how the fireteam should work and what can each class do to help. You can choose the class that fits you the most.