To clarify, the OP is comparing Texas MBA in DFW with SMU, not UT-Dallas MBA to SMU.
McCombs is undoubtly the preeminent MBA program in Texas. But in this case, you should inquire about the career services of both programs. Since McCombs is based 3.5 hours aways, do you still have access to the same career services? How do recruiting events work? Do you get the same degree as regular McCombs Evening MBAs?
My feeling is that the part-time programs are geared toward people who wants to move up the corporate ladder within their current employer, so career service is minimal. This is fine if you want to stay with the same company and move to middle management, but if you want to switch careers after you graduate, see which program will help you do that.
As far as 5 year down the line. I think where you get your degree matters only a little, what you did in that 5 years matters much more.