1st: ask your doctor and or a sports trainer at your local high school I'm sure they deal with athlete's asmtha all the time. I don't know but do you really want to rely on drugs to complete a workout, maybe there's a way to train to reduce the problem naturally.
2nd really depends on your effort and I wouldn't worry about the slight calorie differnce. Hills will
build muscle better for sports but are harder on your joints (going down hill). I'd mix it up so you're not passing the same scenary every time.