I think it's important to adjust to the situation you're in. Sometimes you'll find yourself with a great tank who seems like he never needs much more than a regen. Sometimes you'll get an idiot wearing strength accessories pulling entire floors of mobs in his DPS stance. Keeping on your toes is the most important thing.

A WHM specific tip I think is handy is keeping your oGCD's on cooldown as often as is feasable. This is not saying to waste them, if you know you're seeing a tankbuster soon leave Bene alone so it can do more work for you, but the thing that sets WHM apart right now is the potency of its oGCD kit. The more you let them do for you, especially buffed by the lily gage, the more mana and GCD's you can spend on DPS.