My older son had terrifying asthma, so I feel for you. Nothing quite like going from fine to blue lips in a couple of minutes or standing in a warm shower at 2 AM hitting your child n the back with a cupped hand trying to break up a mucous plug!
There are several preventative drugs, so I'd be hard pressed to keep my child on something that is causing a mood alteration. Have you talked with your pharmacist to find out what other drugs are available that may be in a different family of drugs? I have found the pharmacists to be a valuable resource so that i can speak with the docgor and share what ive learned and what I'd like to try.
My son was on Advair, and it helped a lot. We went from several ER visits a year to none. My younger is on Singulair. Since using the preventative drugs, we haven't had to use prednisone except one three-day burst last summer.