DPS feels repetative.
Tanking does to to an extent, even with the new active mitigation model.
I like the unpredictability of healing honestly, keeps me alert and interested.
This, also the knowledge that I am basically the cornerstone of the group.
Yes, if a tank is undergeared it is going to make my job much harder.
If DPS don't perform it will make my job take longer, or make my job harder if they choose to take unavoidable damage.
But the fact that I feel like I can actively make an immediate, positive difference in the group's success or failure is what keeps me healing. Those moments when I pull out all the stops and I'm 100% sure it's going to be a wipe, but my sheer stubbornness and "Not today!" has us pull through.
If I get acknowledged for it, all the better. :)
I still enjoy the active leadership you get with tanking (in a way, in that the tank leads off the pulls most times) but the passive leadership of healing is nice too (in that the group cannot move ahead successfully if you do not have the mana for it). I don't enjoy DPS because I don't really feel like I make a huge difference to the group. I feel expendable.