Either of these bowls/cities have their pros and cons, but both would be a great trip to make. Reliant is the nicer facility, and is indoors (we even kicked around the idea of playing our home games here for a season while Kyle Field is being remodeled), but the Cotton Bowl is more historic, although a bit run down and in a part of town that has seen better days. There's plenty to do in each city, although I would give Dallas the edge in attractions. Being from Texas, I would be glad to offer advice on where to stay, what to do, how to get around town, and anything else you might need to know once the selections are made.
I've noticed that the projected match-ups for these two games are Baylor and Texas Tech, which, quite frankly, are among the worst fanbases in college football. Being quite familiar with competing against both teams (until their women's tennis team won a match, Texas Tech had not beaten us in ANY sport for over three years running, and we soundly dominated Baylor 55-28 in football during Griffin's Heisman year, not to mention having a recent 13 year winning streak against the cubs), I will do my best to fill you in on their peculiarities and give you plenty of smack talk fodder for either opponent you face.
People from the south plains of Texas are generally honest, hard-working, down-to-earth folks, that is, unless they attended (notice I didn't say graduated, as many major in beer pong for a semester before heading off to careers in pizza delivery) Texas Tech during the past 10-15 years. While Tech used to be a decent regional center for learning, it has since fallen to the status of the safety school for Dallas kids who didn't have the grades to make it to one of our state's flagship schools. Finding themselves in the untamed west for the first time, there is a sense of lawlessness which comes with donning the scarlet and black, and also a sense of built-in denial that their school is located in a place where duststorms are not uncommon and a fear of loosing accreditation is a very real possibility. Do not be surprised to see Tech students inserting profanity into their school's alma mater, tearing up the bleachers in AT&T Jones Tractor Pull Stadium, throwing objects, spitting, or otherwise behaving with belligerence when roaming in packs. If you are interested in learning creative new uses of profanity or partaking in a discussion as to the merits of Skoal versus Copenhagen over some Keystones, this might be the place for you. There's a reason that they have to play a public service announcement at the beginning of every home game about how to behave, or why shirts have to be printed pleading for students to sing the correct words to their song (hint: the official version does not include f-bombs).
Baylor, on the other hand, has had a recent run of success in football, meaning they no longer have to base all their smack talk on women's basketball. By recent run of success, I mean that they have broken their average of fewer than two conference wins per season since the inception of the Big 12 by winning a few games over the last three years. They also had a Heisman-winning quarterback, yet cannot seem to fill their measly stadium, even with the success. The attendance problems are so bad (by the way, Waco is a town of 200k+ and is an easy drive from Austin and Dallas) that they tarp off the endzone bleachers so as not to be embarrassed by the empty seats. Baylor is like the annoying "friend" you had as a kid who your mom forced you to play with, but would always try to tell you how great they were (even though they wet the bed at your sleepover), and who would tump over the Monopoly board once you started winning. They have a confused identity - they claim to be a Baptist school, and talk a good game, yet they harbor girlfriend-beaters, murderers, cheaters, and the like (seriously, look it up). The're basically the same stock as Texas Tech students, although their parents had a few more bucks to throw towards their education at a mediocre school, and they are more likely to be at a coffee shop for a "prayer meeting" than at a dive bar. Unfortunately, money and piety can't buy everything, including a decent fanbase or a bowl win.
Good luck against either of the two. Please note that the above caricatures of Texas Tech and Baylor were made (mostly) in jest, and although there is much basis in fact and actual events, you are not in imminent danger of having goalposts shoved into your seating section or being threatened with a lawsuit, so don't worry too much. Enjoy the game!