Thieves are mechanically simple (a little more complex than guards as you should try to make good use of fields and leap/blast finishers). They are also the fastest class in the game and I think one of the most important classes to roll if you want to get better at pvp. Understanding thieves is very important when fighting thieves. (mesmer too, but I found it easier to understand mesmer as a thief; my first character and longest main) Its lots of fun, and there are some decent build diversity (about on par with guard).
Give it a shot in pvp, and see how you like it. Otherwise, ranger is even simpler mechanically, and very fun. But I think theorycrafters enjoy ranger more than anyone. I loved planning builds, etc on my ranger, but for me, like guardian, I got bored eventually.
I grew tired of thieves, as I wanted a main that could build tanky if I wanted. thieves are very hard to kill (or die as) if they are on their toes, but almost all builds are pretty squishy when you are feeling lazy. (unlike ranger)
Rangers have to deal with a pet though, which is where a lot of the difficulty comes in. You can ignore it mostly though, but if you want to play at the top of your game, you’ll need to start playing with the pet. Still easier than making careful use of smoke fields.
This is my favorite build with ranger, but its a little harder to master than most ranger builds. (however when you do you become invincible)
http://gw2skills.net/editor/?fNAQNAR8YjMq0yaJLesQ1aALhqdDEAjKrm19GEt3cBbqA-TJxHAB1eRAQqMwJ7PAwTAAA
Engineer is a class that can also be fast, but most of their stronger builds are more complex. However, you can build some simpler builds and they preform quite well. This class has the most diversity among the classes. I currently main this class and play a very simple, yet strategically complex build.
here is the build:
http://gw2skills.net/editor/?fdAQFAUnUISbX23F2UBrXGJvgG9VOSNBdAy3CEVAB-TJBFwACeAAI3foaZAAXAAA
Good luck and try all of them in heart of the mists.
