Bigger isn't necessarily better
Of the four companies you listed I've only applied to one of them: Northwest.
But the major of my choice would be Alaska. Why? Because of the lifestyle mostly. If I needed to commute it would be fairly easy.
Also the mostly North-South route structure is brilliant. The summer Alaska season is balanced with the winter Mexico season.
Sure Alaska has their problems but not like UAL, DAL or AAL. I'm just not interested in being one number out of 10,000.
Fly safe!