I prefer micrometers over calipers any day.
Maybe this is not the way most gunsmith's work, but as a toolmaker, I like to have a surface plate, gauge blocks, dial indicators and all the normal machinist tools for measuring height off the plate, plus a milling machine, lath and surface grinder & a grinder vice for holding things squarely. I have often used ALL of that stuff doing gunsmithing for myself, and in my experience, working like a toolmaker would do things, makes it easy to do a better job than most gunsmiths do. Guns are manufactured in a machine shop environment, and IMO too much work done with files & by eye, just screws up a gun. The proper "machine shop style" approach & tools makes your workmanship look like a factory job instead of a lousy hand job.