I think that some of you are are making the mistake of looking at Angelus and thinking "Angel," The reason that Angelus avoided the confrontation in the hospital is the same as why he was hiding in a coal mine in the flashback in "Fool For Love" a couple of seasons later. Angelus is NOT a fighter. Given a choice, he runs. Sure, he could have probably killed Xander, the police, and whatever hospital staff decided it lend a hand, especially if none of them except Xander (who would have obviously been the first one to die) knew that he was a vampire, therefore would be totally unprepared for his strength and speed.
And, just to clarify, don't think that Angelus' reluctance to fight unless cornered is due to any lack of skill. He CAN fight, he just prefers not to. It isn't his style.