I've been their about 4 times. I've sat in the upper deck once and personaly their is no bad seat in Texas stadium. but of course you want to get as close to the game as possible. I've gotten tickets on the lower deck about 18 rows from the field and the view is great. Stay away from the "sun sections" as i like to call it. the opposite end zone from the Cowboys tunnel. If its a afternoon game the sun is blinding. The scections you might want to get is from 1-5 and sections 32-36. somewhere in that side. The endzone seats are a little cheaper and the tickets says row 30 for example and your actually in row 18 or somewhere along that area. Non the less, anywhere is good expecially this year, since its their last year thier. Get the tickets asap, the closer the date the more expensive.
For me personally the closer to the action the better. If you can spend the $$ I would try to get some corner endzone seats first few rows. I have sat there several times and it is a great experience. I would try to stay in the lower level. Anywhere in the lower level is a descent seat.