Q:
Which caster profession should I go with?
Any character I’d always make asura or human from now on. I’d suggest you to do same, these are the best to play on.
From these light proffesion each is unique. Necromancer has pretty good condition damage skills. Mesmer hides behind illusions and with cannon build deals extremly high damage without getting any close to opponent. Ele had decent far skills + supporting ones (healing, slowing enemies) and D/D (dagger & dagger) is known for high mobility and pretty fast attacks.
Personally I don’t see anything special in necro. On PvP it’s not any strong profession. I, for example, play D/D ele and enjoy it very much on WvW.
I’d suggest that if you want to attack from far, mesmer will be better. But if you want to tank and run around, D/D ele will be something for you.
Depends n how much effort you want to put into this alt, elementalist are great for support but are also the toughest class to master, that being said it is extremely rewarding to play
Mesmers are probably the best DPSers of the light armor classes and have some unique mechanics to their play style, with a very good variety of builds to try out