Sorry - I know this is a bit of a boring one, but I assume others must also have this issue.
I'm in a reasonable, if slightly frustrating, job. The area's interesting and useful, but I don't get to do very much of the useful or interesting stuff, IYSWIM. I'm very much playing second fiddle to people who in many ways less well-qualified than me, and I get very little autonomy, etc.
The reason I'm staying is that the pressure levels are much lower than in other jobs within my career. I can escape to go to school sports days, pick up the kids at short notice if they're unwell, eat with them in the evening, choose my annual leave days....
But am I going to regret all this later, when I'm years "behind" the people I started out with?