Any specialty in a big city is going to have lower salary because of the “desire to live in a big city”; also in bigger cities you if you do a “generalist” specialty you will be quite limited in what you do. That’s probably true even for medium sized city too, because many of these places will have large tertiary health systems that are eating up anything but the largest PP and those are getting bought out by private equity. I live in a medium sized city and am a urogyn and since I started 1.5 years ago, nearly all surrounding general urology and obgyn send me anything to do with urogyn, same will be true for IM and FM, you’ll just be doing the PCP stuff. You can basically find a job in a “big city” or at least 20-30 minutes from a big city, in the majority of specialities, even probably Rad ONc and Path. But Irrespective of specialty there will be trade offs, lower salary, more sub specialists, if surgery specialties will have to deal with “minimum volume standards”, not to mention housing costs, grime and crime, parking issues etc. Most 20–35 year olds, especially single ones, have strong desire to be around the cultural centers of the world which is absolutely what they should want, lots of fun to explore, get to know yourself and other people better, etc, but after 35 in many (not necessarily all or most) that desire wanes and you just want a quiet street to raise your family on.
so while market considerations are important, you should pick specialty predominantly based on your interest because you can in general change your living circumstances a lot easier than you can change your specialty once you’ve completed training.