I have used BWI Airport taxi one time, and will never use them again. Maybe we just had a bad driver, but it was enough to turn me off forever.
Our driver made rapid acceleration, quick stops, and took corners very sharply. He also drove with the windows down and no air conditioning on in the middle of July. Needless to say, we were very uncomfortable for the 25 minute ride home. Once we got home, we were thankful to be alive, and therefore didn't tip the driver. He gave my husband a hard time about that.
We would have been better off renting a limo to take us the short distance.