Q:
What level 80 to level next?
A:
Mesmer can definitely be very survivable and have tons of viable builds for sure, and if done right can be a great asset to any team as well, but can be tricky to play in the start, but really most if not all classes fit those 3 words in gw2, the question is more how do you want to go about being useful, and how you want to be survivable
Warrior, if played right Ranger*, Necro has a huge amount of HP.
*Kiting
Holy cow Elementalist. Variety? ya. Survivability? ya. Usefulness in teams? if you learn it, ya.
Oh my god Engineer. Variety? equip a couple of kits to swap, and ya. Survivability? definitely do-able. Usefulness? yes, a plethora of control and the options to buff/heal your team.
Definitely Mesmer (reasons ought to be obvious though)
Thief! (well I’m biased, Thief is my favorite main class)
Know what? Just do them all!