a few thoughts.
there will be unhappy residents everywhere. i am a student at UTSW and i can say that there are plenty of very happy people here. with a program of almost 72 residents, the unhappy ones tend to make more fuss than the happy ones. the work is hard and you will likely be working very close to (but absolutely not over) 80 hours a week for the majority of the residency. but again, you are probably not scared to work if you are picking OB to begin with.
that being said, the faculty here have established themselves as some of the most supportive OB/GYN mentors anywhere in the country. the clinical volume and experience is unmatched by any program in the country. and for those naysayers who say that it is an OB heavy program (~16,000+ deliveries a year), many steps and new facilities have made the GYN experience much better than it used to be. their "numbers" are good and offer more than enough training to be a very, very well trained OB/GYN physician.
without a doubt, a resident from parkland hospital can handle pretty much anything under the sun by the time they've finished their training.