A degree in anything would be good, even one in aviation. Whatever you do, make sure it's in a subject area that you can enjoy. I'm actually pretty pleased with how things have worked out for me so far; if it weren't for my BS in aviation, I wouldn't know that I wanted to get a MS in an field that somewhat relates to an aviation topic (wx).
People have mentioned that seniority is of prime importance. I would agree, but only to a limited extent. Seniority is everything only to the point that your company stays in business or you can deal with the airline lifestyle or if you have a high enough number to avoid a furlough. Otherwise, I think it's pretty much useless. If the above conditions are met, then it could be good, but I think it's important to mention that there are more than a couple scenarios where it wouldn't mean a whole lot.
I'm not sure what the regionals are wanting as far as a degree right now. They all list a 4-year as being "preferred," but they also list 1000/100 and we know that only a couple of them are holding to that.
Anyway, hope that helps.
-Goose