To be a Thief?
If WvW is your thing, I would take a second look at the other classes and make sure that you really like the Thieve class. Personally I feel like a bit of a burden to the team in fights that get to more than 10 people a side… and kind of regret that I didn’t log in with my Guardian or Necro.
However if smaller scale action in WvW is your thing, than Thief can do a pretty decent job there. Soloing camps, killing dolyaks and then getting out before the enemy response catches you is what the Thief excels at. They are also phenomenal at killing noobs and people who otherwise don’t understand the Thief class… but I wouldn’t rank this last quality very highly as that strength against noobie players simply does not exist against anyone who has a Thief alt, and therefore knows what the squishy little thief is going to do once he turns invisible.
In short, make sure you like the class, and don’t let the “thief OP” posts sway your confidence in the class. That said, Thief can be a very fun class, and if you know your stuff you can be useful with it.
As for Thieves in PvE, recently I’ve come around to appreciate a Thief in my party, but you really have to know what you’re doing to be as useful as just another Warrior or Guardian.
In WvW, thief is one of the best classes for roaming and 1vs1 situations, and if you like to be the “scout” of your group, then you won’t regret playing thief. But in team fights, thieves aren’t that useful because they can’t contribute with their team as much as other classes can.
You can make it work in PvE, but you will never be a warrior or a guardian. Our DPS against a single target is really good, but we lack of AOE damage unless you run with a shortbow. Other classes can do a lot more in dungeons than us, mostly because we lack of support abilities (Shadow Refuge and stealth revives are an exception).
But even when we’re not the best in PvE, let me tell you that thief is my favorite class, if you can evade most of the damage while still doing great DPS, your team will appreciate you.