THF: Innate AOE makes it pretty much the best for leveling. Single-target DPS falls off at endgame compared to other styles, making it less advantageous for min-max endgame play. Also gets the biggest multiplier from mainstat, so gains a little more if you have tomes, optimized gear, stat PLs, etc.
TWF: Best single-target damage makes it good for endgame applications like raiding, especially when you can double up on Dino Bone weapons for two LGS effects. Lack of AOE makes it tough for leveling, and its a bit more backloaded to get to 80-100% offhand strike chance. Really needs to be paired with a trance since it only gets 1.0x / 0.5x stat to damage innately, but can leverage imbue and sneak dice much better.
SWF: Nice balance between the two. Better stat-to-dmg than TWF, better attack speed than THF and can still use the offhand slot in various ways. Can use AOE special attacks and feats better than TWF to add some multihit for leveling (TWF only uses mainhand weapon on AOE attacks). More feat-needy, though, since you'll usually need to tack on Offhand Vers and Knights Training or Swords to Plowshares.
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Repeaters: High ROF makes them great at early levels, though its slow to move between targets, so you're often overkilling trash mobs and waiting to kill them one at a time. AOE shots in BE help with that a little now, at least. Falls off in late Heroic and early Epic, then catches back up once you get Expanded Clip, then falls away again towards endgame as the -66% Doubleshot penalty really puts a ceiling on your progression. The slow attack cycle, but 4 shots per attack cycle, means you can really get a lot of punch out of non-AOE special attacks like Sniper Shot or Hunts End.
Dual Xbow: Steady leveling through Heroic and Epic. Good balance of ROF and target switching. Great imbue damage. -50% Dshot penalty hurts them in Epic and into endgame, like Repeaters, and they have no corollary to Expanded Clip to make up for it. Also is the worst ranged style to try and use any AOE shots. Needs IPS the most still of any ranged style. Great weapon options for leveling (Ratcatcher -> eStorm).
Bow/Thrower (VKF and Shuriken): Slow leveling, highly single-target, even with the AOE shots (which arent OHKO AOEs past early Heroic, so you're still finishing mobs off one at a time). Gets really good at endgame, as they get multiple channels to boost their DPS (mainstat, doubleshot, RP, attack speed) that arent penalized and can really leverage endgame stat inflation