Pathfinder: The fastest class, great at chasing the enemy flag carrier and at grabbing the flags themselves.
Sentinel: The sniper class. The sniper rifles are the only primary weapons that are hit scan that I know of at least, I have not used all the weapons yet. Great on defense for calling out and shooting the enemy flag carriers.
Infiltrator: A stealthy class, can turn invisible for brief periods of time. Great at wrecking havoc with the enemy defenses or destroying their generator
Soldier: An all around class, great at defense or offense, but not being the best at either.
Raider: The class I play the most currently. Great at destroying enemy defenses and clearing the flag stand, giving your Pathfinders room to come in and grab the flag without being killed.
Technician: Can repair base defenses faster than anyone else and deploy turrets that will fire at any nearby enemies. Great base defender.
Juggernaut: Heavy offense class, has a mortar that can be used to shell the enemy flag stand and keep it clear.
Doombringer: Heavy defense class. Can deploy force fields and mines to kill incoming enemy Pathfinders. Has a chain gun to spray and pray with, as well as a missile launcher to shoot air borne targets or vehicles.
Brute: Not super familiar with this class as I haven't unlocked it, but serves somewhat as a close up Heavy Offense class with a strong spinfusor, and the area denial
From time to time, I'll probably write more in depth class pages, beginning with the Raider and Doombringer as I play them the most, so look forward to those.
As always, if you're interested in trying Tribes out, it is free to play, so feel free to sign up using my referral code and hop into a match with me. I nearly always play in public CTF games.