I guess my questions would be what is the better metal in and out of SYR? The hub to DFW are all going to be big mainline style planes. If it is all RJ for both DL and UA I'd go with whichever had F and better Y seating. If you get free upgrades on DL it doesn't matter much if half your flights are all Y seating. In addition, the flights in and out of DFW on DL (and UA for that matter) aren't going to be the easiest upgrades for midtier travlers during business times (Sunday/Mondays - Thursdays/Fridays)

It looks like a decent amount of the RJ flights in and out of SYR (mornings/evenings - not mid-day) are at least RJ700 which have F and E+ seating. As for routings, without a 500 mile minimum the atl connection is the best option, and the ORD/IAD are both pretty even. That said, with 500 mile minimums the IAD connection gives ~1675 EQMs each way.

But you miss one option that might be viable (I haven't looked and don't know much about AA) but AA might have a non-stop straight to DFW. It's 1336 miles and you'd earn low-tier status in ~9.5 round trips. I know AA offers some sort of challange that will give you status quicker that might be good.