I would recommend looking at the bases available at each and choosing where you would like to live. Commuting is OK for a short time, but over the long run it can really make an OK job turn into misery.

I don't really know anything about Piedmont. Mesaba has a lot of potential for growth and upgrades, and if you get hired in the front of the wave (which you are) it can be good for getting quick FO seniority which can make your schedules very nice (14-18 days off), and give you a shot at a reasonable upgrade (1-3 years).

Of course, nothing is ever guaranteed in this biz until after it has already happened.

Good luck with your choice.