I'm usually a DPS class, but that's not to say that I necessarily like those classes because of the huge damage or numbers they throw up on the scoreboards. I love DPS classes because I love playing rogue and mage characters. Rogues--especially in MMORPGS--have the ability to go invisible. And I love that. Seriously, there is nothing cooler to me than having a character that can, with the press of a button, disappear from sight (AI and player alike) with the touch of a button. It's really, really unnerving in duels to start off by just vanishing and strafing around the peripheries of the battlefield for a couple minutes until the other guy decides I'm not a threat anymore, sits down, starts chatting with his spectating friends and then SPLURCH, knife in the back. Don't yell at me; that's what a rogue would do.
I love mages because they're usually very light, mobile, deceptively dexterous and can lob fiery death into the middle of the fray. Just being able to pick my battles and if things go sour being able to teleport my clothy ass out of there is really a boon of the class.
I've done healer before and enjoyed it. Actually, I've never, ever had anyone complain about my abilities as a healer and have actually received a lot of compliments because I take really, really good care of my party members, but it's just not my thing. Tanking is my absolute, bottom-of-the-barrel, most hated niche to fill. I did it once in Nexus: the Kingdom of the Winds when that was still new (and no more popular than it is today) and it drove me insane watching the mages paralyzing everything and the rogue teleporting all around the enemy they were meleeing, popping in and out of invisibility, while I just stood there with my best self-buff on and swung at the most dangerous-looking thing. Bless the tanks out there that make my roguing job easier, because it's a job I will never be able to do.