Dallas marathon was canceled a few years ago because of ice. Hate to say but there's a decent chance [15% maybe] of bad weather that makes it miserable or even canceled.
All that said, I did the dallas half last year and thought it was great. It's huge with 20k plus runners, big tv screens and fireworks at the start. Great course support w lots of aid stations, some bands and other entertainment on the course, and a decent # of spectators.
I'm doing the Dallas marathon (full - my first) in December. I live in Dallas so that made it an easy choice. If I had to fly to all of them I'm not sure it's the one I'd pick.