Mesmer Vs Necro
Mesmers are very trait reliant, plus a few skills are “Not entirely working correctly”, so low level play with them can be nothing short of painful at times.
A good thing to do would be to jump into the heart of the mists and mess about with some of the traits and see how you like the class plays.
If not, make another character and do the same.
It all comes down to you having fun with the class or not.
With the new trait system, leveling a mesmer will be a pain. Don’t get me wrong, it was always a tougher class to level, but with master traits locked until 60, most of the leveling will be tedious and slow, even slower than before.
Leveling a necro is a breeze compared. Put on two daggers and auto-attack everything dead in a few hits. Or go minion master and watch tv while the game is more or less leveling for you.
You can have more than one character, so my advice would be, try the necro for some levels and see if you like the playstyle.
I have both at 80 and I think they are fairly interesting classes at cap.
Too bad the leveling guide in my signature is outdated, otherwise I would have offered you my help on leveling a mesmer.
The Leveling & Open World Compendium
Create both professions, go spvp for a week, decide what profession you like best, use tomes to lvl to 80..
goodluck.
E.A.D.