Guild wars is one of my favorite games. All the professions have their own pros and cons. Here are some resources to help get you going:
http://wiki.guildwars.com/wiki/Main_Page (be sure to check out their description on the professions)
http://www.gwpvx.com/PvX_wiki (good resource for builds)
http://pvx.wikia.com/wiki/Main_Page Assassins: These guys are hit and run, and are popular for doing speed clears. The downside is that they take a lot of practice to get good at.
Elementals- typical dps class. One of the most popular builds for them is running a searing flames build. They are also frequently used in elite areas for bonding players.
Ritualists: These guys are cool. They are frequently used for summoning spirits and having them fight with you. Be sure to get the skill Signet of Spirits. They also make decent healers and can buff other players with weapon spells.
Warriors: Your typical tanking class.
Dervish: They are basically mystic warriors. They use scythes to help chop down their enemies and use enchantments to compensate for having a slightly weaker armor then the warriors. Their main goal is to put pressure on the enemy.
Paragons: These guys have been nerfed badly, I don't recommend them. Their specialty is buffing other players.
Mesmers: As someone who plays an elemental, these guys are my biggest pain in the rear. Their specialty is shutting the enemy down and countering their attacks.
Monks: Typical healing class. They can do some decent farming too if you are willing to run a 55 build
Rangers: These guys are pretty flexible; shut down, beast trainer, pressure, etc. They are basically the jack of all trades.
Necromancer: They get their power from the deaths of their enemies. They are good at punishing the enemy by really weakening them and decreases hp. They also can summon the undead and run a minion master build.
Regardless of what class you choose you still have a lot of flexibility with how you play. All it takes is a little bit of patience and creativity. This is just a basic overview and it really does depend on how you want to play. Are you a mid-liner, support, or like being in the front line?
My main toons are ele, rit, and warrior. I like being the nuker.
edit: While prophecies may take the longest to get through at the beginning, you can easily skip the first chapter by getting a run to lion's arch. From their you can get to other campains and EoTN. Plus, you get your heroes early.