Thread mikes win hands down, the ones that I have, I bought on e bay relatively cheaply, they have fixed anvils, and are in the more common pitch ranges; I also bought Polish made interchangeable anvil sets up to 4" but sold them along with my business; thread mikes are fast, accurate, and read directly in pitch diameter, no calculations necessary, just look up the thread specs in Machinery's Handbook --- and go at it. Having said that, I agree with most of the other comments, you most always just fit a thread to a nut; one thing, 'tho, best to run a sharp tap through the nut first to eliminate possible burrs. About the only time I bother to use a thread mike is when I'm making a thread (plug) gage to use for gaging a internal thread to be cut in some pitch or diameter that I do not have a sample to use as a gage.
I also have triangles and wires, but hardly ever use either. One old machinist that I knew once brought a job to me to do, with wires to gage the thread, they were all that he had to do the job, made of baling wire! They worked well enough ---