I have very little experience with Necro, so I am only repeating what I've heard - extreme survivability - perhaps the most survivable profession there is, depending upon the player - including Guardians. Again, this is from forum spew, so take with a grain of salt. Necro WILL be my next character's profession.
My ele was an experiment. I loved my thief due to the adrenaline of being all over the place, backstabs, teleports (shadow walks), etc. He was a bit squishy, but I liked the mobility.
Upon suggestion on their forums to try elementalist, I did AND HATED HER until such time as I got used to button mashing. It's kinda the same feeling as learning a DDO monk the first time.
Once I got the keys down, I have loved her more than I ever did my thief. Though she was squishy at first (say first 30-40 levels), she seems to be much tougher than my thief now at 80 - which I find odd for a caster.
I am seriously contemplating dumping that thief now, but I gotta get another character leveled on the crafting skills he has first

EDIT: The only thing I complain about on my Ele now is underwater skills. They use a lot of AoE.
That's fine if you are supporting a group, but I tend to play
with by myself a lot.