I have played them all. You have already played one of the most flexible, the Mesmer.
Warriors burst damage is insane, especially if you spec something like GS and Axe/Mace with fast swapping, but you also have to develop a good sense of when to bail out and run for those times your outnumbered and all you good stuff is on cool down.
Guardians have a bit less damage but take less damage and have a very broad range of utilities to fit every situation. Between the two, Warrior requires more skill dodging to keep alive, while the guardian has a wider margin of error.
Thieves can have some insane burst, but as a personal choice, I found them to be one trick ponies and I got very bored with that one trick.
Engineers and Eles are classes I consider to have very high skill ceilings. They both have so many skill options, they are like those circus plate spinning acts to me. If I ever get really bored I may re-roll one of these and seriously try to master them. I know I got my Ele to 80, but felt like I had only scratched the surface of their power.
Rangers could be the strongest general map soloing class. I know I got my world completion title using my Ranger. Like a mesmer, having a summons (yer pet) to distract foes comes in very handy especially on any of the harder skill points. Pet choice based on the weaknesses of type of mob you are facing is key along with developing skills with all the weapon sets Rangers have, not JUST bows.
So, out of all the classes I think Guardian and Ranger are the best for map exploration and completion. Warrior gets an honorable mention if you want to farm (kill the stuff FAST).
Edited by beadnbutter32, 09 August 2013 - 11:38 AM.