My main right now, and I suspect my favorite class in the game, is the shaman. I love their healing power, I love their totems and their recent rework, and I love blasting people off cliffs with Thunderstorm! But in reality, what use would a shaman's skills really be? Healing is great, of course, as is the power of reincarnation, but it's on a really long cooldown, so I'd worry that if I used it at the wrong moment, I'd be dead for real. It's happened enough times in-game, trust me!
And while thunderstorm would be an awesome skill for times when I'm feeling a bit panicky and hemmed in by a large crowd, I suspect I might get into trouble for blasting people 30 yards through the air.
For me, I reckon it'd be either a mage or a paladin. A paladin, because of the bubbles, and Lay on Hands. Not only can I make myself invulnerable, I can make my friend invulnerable to physical damage, too. And if that doesn't work out, one of us can go from 1 hit point back up to full health in a single global cooldown. And mages? Well, that's a selfish one. They can't resurrect or heal, but they have slow fall, and portals. The portals are the number one reason why I'd roll a mage. Just imagine, you can move between major cities on different continents with a portal! Amazing.
So, how about you? What class would you be, and why? Equally, what class would you never be, and why? For me, that class would be rogues. I hate the picking only battles you can win and sliding into the shadows when things go wrong.