DPS/Healer/Tank in that order
The reason I prefer DPS is because they usually have the coolest spells/abilities. They also can be the most fun for making cool combos.
Healer is second because support roles always hold a special place in my heart.
Tank is last, even though I still enjoy it. It's very difficult and whenever the raid goes sour, you're blamed for causing it to go sour. For example, if some goofy damage warrior pulls everything in a raid and you were still at the raid table waiting for everyone to get well fed and boost up. You shouldn't be blamed for the incompetence of the person who prematurely pulled everything. But no, everyone blames you for not taunting because of that moment and letting him die.
Tank, no one else knows how to raid properly and its pretty loving annoying when half the people in your clan have green/blue gear at lvl 90 onward. Its like no one knows how to farm mystics anymore.
This applies to all mmos btw, not just wow.
For the tank problem, that's how I feel about it above.
However the other issue...
Play in a different clan, if they are too incompetent to actually not be able to farm up for purples/full raid sets, they are not worth your time. I don't see that problem at all in ours and we raid regularly. We do weekly mystic pandaria transmog runs/highmaul 10-man/BRF 10-man every week and we do just fine. We are also starting to do mystics now that we have people to do it.