I hope my response can add a little of bother worlds to this thread.
12 years UAL. resigned my seniority to go corporate(fortune 25.
I was 1/2 way up UAL seniority list when I resigned shortly after 9-11.
Corporate after 10 years was great pay and what I would term great long term stability at this department. All true in the stability department except for one thing I thought would never come into play, a boss who could turn your world upside down overnight. Here today gone tomorrow. The definition of a true at will employee.
About 300-350 hours a year, 60%international. All the great perks everyone mentioned. Good Amount of time off but you never could predict your schedule more than 2 weeks out.
I'm now back at UAL. PART 121 operations are mundane compared to the 91 world where you are doing lots more. I will now commute and be gone more.
However, I miss the security of an airline and a union. I realize furloughed pilots might say otherwise. As I found out the hard way, job security in the 91 world is a reach at best. Best to you.