Good question.

Delta has just as much schedule flexibility as Southwest. Southwest has the advantage of more trips to trade/domicile flexibility, Delta has the ability to drop trips using blue-slip or IVD, long call reserve, and more varied mix of flying. While you can fly the FAR limits at Southwest and beat any legacy pilot's W2, for you average line holder who picks up open time at either income will be similar. For those that claim they only want to fly the 737, you'll advance in your seat faster at Delta as those above you bid off to bigger equipment.

I seriously looked at it twice. Southwest hired me first so my seniority started growing here and as time advances it makes less and less sense to leave. Also, the first time around was during a time when hiring was competitive and advancement was slow. I was looking at a good year of commuting to a junior base to cover three airports. Unfortunately I drive to work at Southwest and while Delta would be a very easy commute, by a very small amount it didn't make sense for me. However, if I could go back I would have taken VSP ($500k would have tipped the scales) and would be close to holding 330B in DTW (more senior than the left seat at Delta). As mentioned above, I'm approaching ten years here now and in the left seat so leaving now would never make sense.

Whenever someone says "I would never want to work for United/Delta/America {insert some coping rationalization}" or "I would never work for a legacy" my spidey sense goes off. All are good places to work (well I think AA ranks below SWA/UA/DL), so everyone should pick the one that works best for their situation. I would also never believe a pilot that works for company A that tells you company A is the best. Most pilots want to rationalize they made the right choice.