Here we go. I am sure you will get the various sycophants for different airlines responding.

But I think you need to analyze the routes you will be traveling, and select the airline that serves you in that regard as your first criteria. If that is a toss up, then you will have to weigh all the subtle differences between the programs. The basics are the same.

For me, I selected United because:

1)Years ago, when I decided to focus on one airline, United serviced more of the routes I needed.

2)The extra room Economy plus seats is very useful, especially if seats next to you are empty. Also, the aircraft are newer than many others.

3)United has the UGS status above 1K. I am not sure if all the other airlines have a similar program.

4)They have consistently treated me well for over a decade in most regards,
earning my loyalty