Congrats. Two good pilot groups IMO. How long do you have? If no time tell both yes. That will get you till the next few weeks before training and you will possibly know the status of the proposed mergers between DAL/NWA and CO/UAL. That will possibly sway your thoughts. Others may disagree, fair enough, but you are under no obligation to shut either door down until before class. Give them a few days and I guarantee they will have the slot filled. (Virtually any airline will be more than content to call you the day before a class date to rescind the offer, happens. It's business)
If it does go to merger at DAL/NWA, consider best you can the implications to pilot demographics. Should look at same for CO with a possible UAL merger.

Pilot demographics will affect you for the rest of your career (seniority progression which gives you choice about quality of life issues like aircraft choice (pay and routes you like to fly-domestic or intl, etc) and domicile.

Place of residence should be secondary. If you stay in Dallas you are going to commute for awhile regardless of choice. Fortunately Dallas is one leg commute to most anywhere you will be at CO or DAL anyway.
Nice dilemma to have <g>