Okay, I have played many classes. 67 CL, 62 Bard, 56 Ranger, 53 Necro, 51 Mage, 51 Rogue, 40 Ench, 34 Druid, 30 Warrior, and Paladin, Shaman, Beastlord in the teens, Monk, SK, Wiz and Berserker less than ten.
My comments on anything over 50, plus the enchanter and rated from playing and observations in soloing, grouping and raiding:
Mage. Send pet. Nuke once in awhile. Easy. Easy. Easy.
Necro. Difficult in a group only because you are at the center of this bizarre spider web of mana, hit pts, outgoing mana, outgoing hit points, controlling your pet, dotting...I wish my necro had 8 more spell slots. Easy. Medium. Easy. (Necro has a more clearly defined role in a raid.)
Rogue. Don't steal aggro from the tank. Difficult at high levels. (Hard to get a backshot when soloing.) Easy. Easy.
Ranger. Easy all-around. DPS machine that can root and shoot and even has spells to reduce aggro.
Bard. Easy to solo with, especially with the melody command. (Probably saved a lot of us from premature arthritis.) Easy. Easy. The bard DOES take concentration, and song set up is vital, especially in a group/raid situation. Ex. When you run across a caster, you need to change your twist to a resist song, and hot keys are a must.
Cleric. In a raid last night, I was responsible for keeping myself alive, and of course, if I could do that, keep my group alive. I somehow managed, although in one fight I was getting hit almost the entire time. In between healing my group and myself I was spot healing the SA and even people in groups who had no healer and were screaming for heals. In a group, when the cleric dies, everyone else usually follows. However...
I think the enchanter is the hardest, and here is why. When I heal someone, I can push F2 on my keyboard to target the tank, and then number 7 for my Complete Heal button, or 0 for the fast heal. Unless my groupmate is dead or out of range, I can heal him or her. The enchanter sees an add or adds, has to target them, and when they make the unpleasant discovery that some mobs are not mezzable, they get pounded. Clerics can take a beating a lot better than enchanters can. Chanters get my vote for hardest class to play. Can I get C6 now?