Just a personal preference,
Being a huge fan of 757, if I could, I will go out of my way to fly the 757s before they are retired.
There hasn’t being a viable replacement for the aircraft and that powerful engine lift during take-off is still my favorite.
787 has a longer shelf life and with United ordering close to 200 of them including options, I will be on the 787s for the years to come.
I still remember when I was in college watching the news coverage on how 757/767 was going to change commercial aviation with new avionics, more fuel efficient engines and common certification for pilots to fly both aircrafts. That news coverage got me exited about traveling and flying.
Oh, yes, couple who want to a window seat is a no brainer. Same typical United “quality” of food and services on the 757/787…..at least United is consistent that way.