Personally I love Air Tran. I fly four-six times a year with them. Now this past Dec they did change my nonstop/direct flight to one with a layover in Atlanta, but their customer service is great.
If they change your time by just a few minutes, they will let you choose another flight, fly out on a different day, or even change airports for free. If none of those options work for you they'll refund your money. Other than the one time in Dec though, my flights have never changed by more than maybe 30 minutes at the most.
Also last Dec for the first time I saw them measuring checked bags. I've flown once with them since then though and didn't see it. You still need to make sure your checked bag is no bigger than 61" though, including wheels, handles, and any bulges.
Anyway we love Air Tran and are really dreading when Southwest takes them over.