When you get down to it, it's a feel thing and while there are differences, they don't really amount to a major difference that would compel you to pick one over the other. The big one is the jump skill but quite frankly I like them all for different reasons. Ignore people who tell you x class is no good for y activity. In short, write the three classes on scraps of paper, put them in a hat, draw one randomly and play it.

This all depends on if you want to have fun in raids. If you do, just play Warlock or Titan. Hunter is the worst class right now for raids and you'll basically be suckered into being an orb battery for your team. If you don't care about raids then play whatever looks the coolest for you. In the end it doesn't really matter unless you're trying to clear end game content.

Hunters are really good for staying alive on arcstrider while simultaneously killing everything around them with relative ease. While gunslinger cannot buff their allies all that much, they do take the biggest advantage of all the buffs they are given, and can fill the super of their team if they hit precision shots (note that this doesn't require kills to create orbs, only precision shots). Tether is also very good for support, maybe the best at the moment because they can provide orbs, armor and recovery buffs, and turn their allies invisible on one tree. On the other they can keep enemies suppressed for very long amounts of time if paired with the gamblers dodge (smoke bomb, wait till it's done, dodge, smoke bomb), they can also stay alive pretty well with the invis dodge. They can also farm better with keen scout, but this is a minor point. Warlocks have really good support and ad clear with stormcaller, and incredible sustain on voidwalker. I cannot personally recommend dawn blade for anything. Not that it is bad, it just isn't that strong. Titans only have team sustain and ad clear, which isn't bad at all, but you just have a very set role as a Titan. TL;DR: hunters are well made for damage and killing stuff, and they are good for team play with tether Warlocks have sustain, support and ad clear And titans have team-wide sustain and ad clear If you are a solo player I would recommend either voidwalker or arcstrider, but if you are a team player, they are all very strong, it just depends on what role you slant to play.