I think the obvious issue is the higher risk with the major airline, things like mergers and bankruptcies are more possible and there's always the threat of losing your medical. The thing about a GS career is that the benefits are pretty good, you're treated pretty darn fair in a bargaining unit position and you are able to put away a good deal of leave and money for retirement. Realize that with locality and a little per diem, the GS13 starts pretty close to 100K, if you get promoted, another 15K on top. Looking at the pay scales and charts, you definitely won't top out at major airline captain pay, but there are many benefits too, working more than 8hrs is "normal" for an airline pilot. Working over 8hrs (or 40 workweek) as a GS is usually either comp or overtime. Comp time is great. In short, it's nice to not be treated like dirt, as has happened previously at other jobs. It's easier to maintain a healthy lifestyle and normal circadian rhythm. Those last parts are some of the most important to me.