The variety and flexibility offered is so varied that only you can decide what's best for you at your stage of life and career.
Delta just had a first mover advantage, if you want to call it that. AA and UA will match or exceed DL conditions. And regionals currently offer better QOL. The situation is so fluid that what makes sense this week won't the next.
APC
A more US centric forum. Browse till you drop.
And please come back here and give us an executive summary.
Good luck.