UTSW is one of the best programs in the nation. Often overlooked by northeasterners, UTSW has a very strong tradition in academic medicine, including 4 Nobel laureates on faculty. It is probably the strongest program in the state of Texas and likely the southern region of the US. I believe USNEWS ranked it 8th for IM. I interviewed there and found that it attracts the more "gung-ho" types....which was not my style. Parkland is a phenomenal training hospital and UTSW campus is very nice. From talking to residents, interns often cap out on call nights meaning that you are always busy. Thats good if you can learn solely on your feet (no pun intended), but bad if you like to supplement you hands-on experience with reading. Word has it that the outpatient experience is not very strong. As with many of the top ranked programs, residents at this program tend to have an aire of superiority, which is neither attractive nor helpful.
As for Dallas, it is a big, polluted, sprawling city with a cosmopolitan feel and some personality. Its flat, like Houston, but less hot and humid.