Wizards or alchemists are going to be the most popular up through the levels for their AoEs in power levels, but once you get to 60 they take a back seat to petters(Necromancers and magicians) because people will throw 3 in a group and have them sit afk while they pull and loot a insta spawn mob over and over.
Tanks really aren't that sought after any more, through the levels many have taken to tanking lower leveled mobs with a healer or melee class tanking instead of the old style of 2 DDs, a tank, and a healer grinding on higher level mobs. Tanks of course are still big for raids but there's already established main tanks with maxed class mastery points.
Bards or enchanters are always wanted as mana batteries, as are shamans and clerics for their buffs. As for other DDs a monk has good offense and defense and are never not wanted, rangers are also not bad in the damage department if buolt right and they also get a decent enough tick heal that they can cast on others and stacks with a bards heals for a great grouping combo. Rogues on the other hand are probably the least popular as they don't have much defense and their damage is primarily in bursts which isn't the best for a grind.
I would recommend against picking a class based on just what is most likely to get groups, I got a wizard to 60 with a bunch of PLs and I am bored sick of it in grinding, but I love playing my bard or ranger, or my new monk which I've been ploobing with hunt and gather quests for the past few days :/