I have long qt syndrome and asthma. I need a rescue inhaler. Which one has been used most on people like me?

Talk to your Doc. Long qt syndrome and asthma pose some unique challenges. If one has both these syndromes then follow up is needed with both an allergist and cardiologist.
Talk to your doctor. I would probably prescribe Levalbuterol (xopenex) for you, but you should ask your physician as well.