If you really want to minimize long travel days, your best bet is to book a direct flight - either Southwest out of DAL or AA out of DFW.
If you want to stay on Delta, you're probably better off going out of DFW. It's been a long time since I flew out of DAL, but the delta "terminal" was a single gate. I think there was a snack bar. Additionally, if you do face weather or other issues there is only one option out of DAL. At least from DFW you have the possibility of being able to reconnect through MSP/DFW/LGA.