I did the Delta Comfort from ATL to SXM last year and enjoyed it. They have changed it some this year as you have to book the entire outbound or inbound routing in Comfort and not specific legs of your trip. For a little more than coach, especially on a 4 hour flight, I thought it was worth it.

I much prefer Delta to AA/USAir. Immigration in CLT was a mess every time I flew through there and even with ALT being big, it seemed to work a lot smoother. The past 3 years Delta has had a better connection and also price in my case.