Ele or Necro
As far as I know Necros are very welcome in a wvw setting. The thing with dungeon groups not wanting necros is mostly just because others classes may be able to bring more party support, but in the end it depends on the player what a class contributes to a party.
Related to your question, if you would like to have a character to play all aspects of the game with choose elementalist. It’s true, its a bit overwhelming in the beginning with the attunements and combos and squishyness but in the end its quite rewarding.
If you go for mainly wvw Necro is a great option too. You could just test both (for example in pvp) and decide then.
I heard eles are a god in hands of a pro. How are necros in 1v1?
Make both, take them into sPvP and fiddle with them a bit in there. sPvP is the only place where you can effectively gauge a class without having to go through the grind.
Play with a few traits/builds. And learn a couple of combos. See which one fits your style more.
Ele’s are beast. Necro’s are beast. But Thief’s are number one ;p
They are both ok in 1vs1. Elementalist are better right now, but against their counter they will both suffer. Elementalist will drop a bit after january 29th with the nerf to might so we’ll see what will happen. But mostly the advantage of Elementalist is the range of stuff they can do to adapt, while Necro with either dominate profession with limited of condition removal or be dominated by ranged profession (lack of mobility) and cc profession (lack of stun breaker/stability).
In WvW, they are both great profession. Necro are the source of burst dmg with wells, while elementalist are more of a support profession. They both are part of the meta zerg GWEN with E standing for Ele and N for necro.