Try each and see which you enjoy the most. (Or try each and just keep going on all of them. They're each fun in their own way, and this game doesn't place any limitations on how many of the classes you can advance.)

As far as the dungeon queue times go, the most efficient pattern is probably to keep both a DPS class and a tank or healer class leveled to wherever you are in the main storyline. Use the DPS class for the majority of the quests, but then swap to tank/healer when it comes to a dungeon run. Once you get to level 15 (where dungeons start) it's extremely easy to level a tank or healer with just dungeon runs alone. So leave all the other questing for your DPS classes, where they can get the majority of their experience without needing to wait on a dungeon queue. (Well, at least that would be the most efficient if you're planning on leveling both at some point anyway.)