Currently have 5 characters @ 80. Elementalist, Mesmer, Necro, Guardian and Ranger.
Spend most time on my elementalist using staff, because of the 4 attunements, perma swiftness, the massive AoE dmg and combo fields this is one of the best characters for group play (Dungeons, Fractals, WvW)
My friends always want me to bring my elementalist to the party
Found Guardian rather boring but I guess I'm not a melee player. BTW: Blast finisher on hammer rules! yeah

Ranger is ok but much less AoE and much less group support compared to the other options.
Mesmer is fun shattering them illusions gives good AoE dmg, some nice support here aswel (still less compared to an Ele)
Necro is also awesome IMHO. Though perhaps because of no 4 attunements a little less versatile compared to ele.
But the conditions, epidemic, staff skills, wells and minions do make up for that loss.
Really enjoy playing necro. Love the way he looks and love the skill animations and spreading conditions with epidemic rocks!
But perhaps thats becouse in GW1 I mostly played Ranger with Broadhead arrow + epidemic (which was a mesmer skill FFS).
Awesome had so much fun playing that.....
My Advice would be Ele 1st and Necro 2nd.
Haven't really played the other classes yet so can't say anything about those.
next up to 80 wil be my engineer though