Pathfinders are meant for a high-risk, high-reward play-style, either capping flags and running off with them, or blasting things apart at close range. They even have grenades that knock the flag out of enemy hands. They have a Shotgun, a Spinfusor(Gun that shoots explosive disks. The staple of the Tribes universe) and a Bolt launcher, I think it was called(It's a crossbow with explosive bolts anyhow), and a Light Assault Rifle.
Sentinels are the snipers. They've a moderately safe playstyle. They kill things at obscene range, use jammers and such to avoid being picked up by enemy sensors(so they don't appear with chevrons above their heads and their textures are blurred somewhat), and use claymore mines and the like to prevent things from entering their base or hidey spots. They have a couple of sniper rifles, an overpowered revolver that shoots ricocheting bullets and an SMG.
Infiltrators. They're the (you guessed it) spy-like guys. They're awesome at killing the enemy generator and sneaking into places where they shouldn't be. Also, backstabs and sonic punches. Their safety depends on their remaining energy. They've got a stealth spinfusor, an SMG, the Jackal Launcher(a sort of small grenade launcher that shoots 3 grenades before popping them), a pistol and some throwing knives, if I remember it right. Oh, they can also get smoke bombs and sticky grenades.
Soldiers are the usual Jack of All Trades. They can work at pretty much everything, but won't excel at anything. Armed with an assault rifle and thumper(medium-range grenade launcher) at first, they can end up with a Spinfusor and Eagle Pistol(same OP gun that the Sentinels wield), and have armor that increases survivability, and a utility pack that gives them a truckton of grenades.
Raiders are generally an AoE class, that deals primarily with clearing flag-stands of defenses(and pesky Heavy On Flag-s), ripping open base defenses and dishing out punishment to vehicles. They have a couple of grenade launchers, an SMG, a shield pack(damage goes to energy rather than health), whiteout grenades(flashbangs, basically), a Jammer Pack(same as the Sentinel's), and EMP Grenades.
Technicians are a class that usually deals in base defense. Their place is normally either at the helm of vehicles, or in the generator room. They have the most to worry about Infiltrators coming to get them. Their loadout consists of an SMG or a Thumper, an improved repair tool to repair base structures and vehicles, a pistol that shoots supersonic rounds, a Sawed-off shotgun, the ability to deploy turrets, motion sensors and grenades.
The Juggernaut deals in long-range bombardment. They have extremely powerful mortars that can kill most medium and light classes in a single hit, if the enemy is caught in the center of the blast. They're usually used to shell(bombard over a period of time) base defenses, sniper positions, and flag-stands, but their heavy spinfusor and LMG also allow closer-range combat. They have health regen packs, which only add to their immense survivability, they have Heavy AP Grenades, and they can throw spinfusor disks with their hands like shurikens.
The Doombringer is designed primarily for Heavy On Flag duty, killing vehicles and high-flying enemies, and ripping through anything that gets even close to your base with a chaingun. They have the aforementioned chaingun, a rocket launcher that can only be fired once it locks onto something, and a heavy bolt launcher(basically a big-arse crossbow with explosive bolts). They can deploy force-fields that severely damage(and can kill) enemies that pass through them, mines, and of course, frag grenades.
The last class is the Brute. They're generally an anti-infantry heavy class, meant for midfield combat and area denial. They've got a heavy spinfusor, automatic shotgun and a rather large revolver. They've got Light Sticky Grenades, and Fractal grenades(they're their primary area denial tool. Toss one and it'll make bright green fireworks in the area they're in, damaging enemies caught in the blast continuously. It also works well in revealing Infiltrators). They also have shield packs, which allow them to take damage to their energy pool.