I fly PHL to/from TPA weekly and have found the A319s to be enjoyable. I always liked the 737-300s and 400s, but the extra quite A319 cabin and wider isle make a big difference. I also like the flat video screens that open up above the seats to show the safety videos and movies - very high tech.
I've been flying on UA A320s for several years now and had the same opinions there. The 757/767 still are my favorite planes, but A320s/319s are a close second.