What class should I play?
Thiefs are pretty wide in variety in all PvE, PvP, and WvW. However, thiefs are not as effective in a large raid in WvW than they are solo (roaming). Between the two, I would roll a Thief (much more sought in PvE than a ranger in my experience).
Allow me to put bias into play and I’d recommend an engineer, they aren’t AS strong as they used to be in PvP, but with the right build they can deliver swift justice. They are a fairly complex class if you want a challenge, and you’ll never get bored of them. They have tons of support, survivability, and damage capabilities AND you can even call down an orbital strike!
In the end you can decide between all classes. After all you have 5 default character slots! Enjoy the classes
I offer What should I play.
Every class more or less can fit into a group. So really, the choice needs to be played on what you think works best with your play style.
Between Ranger and Thief it’s Thief hands down. The link savacli posted is the best summary of the classes that you could get.