I don't think it makes a bad first impression, it just stresses out those of us who are waiting and don't have any acceptances. I'd recommend contacting the school where you're on the waitlist, and let them know your situation - just say you're still very interested, but you need to make a decision soon, and do they have any new information? You can also contact the other school and let them know you are interested but still waiting to hear from one more place.
I have a feeling there are a lot of people in this position as well...