I personally travel 160 miles round trip to see my Endo who orders a full array of blood tests every 3 months (including TSH, FT3, FT4, vitamin panel) and performs an ultrasound every 6 months (I have a goiter with a prior biopsy).
I have a coworker with my same dx (Hashimotos w/goiter) who sees her local PCP (also my PCP) and her labs are only run every 12 months for TSH only. No ultrasound.
This is purely anecdotal, but in my case I would definitely choose my Endo over my PCP.
It all depends on the individual doctors... some pcp's are very good at managing thyroid conditions, some are not, just as not all endos are good thyroid doctors.
The doctor you choose must be willing to order the proper tests every time you get blood work (Free T3 and Free T4, along with the inevitable TSH), as well as treat your symptoms, not just the labs. The doctor must be willing to adjust Free T3 and Free T4 levels not just the TSH level to alleviate symptoms and should understand that TSH is often suppressed when one is on thyroid medication. S/he must understand that if you have Hashimoto's you will need regular adjustments in your medication to make up declining thyroid hormone production.
As AJ says, not all doctors are created equal and it's worth the effort to get the treatment you need.
Depends on your relationship with pcp or endo. Not all are created equal. If your pcp is not taking care of your thyroid condition, then the effort to travel to reputable endo is worth the journey. I've driven out of town 100 plus miles to discover a reputable physician. Do what you believe is best for you.
In my case, my pcp takes care of my hormone treatments better then endo, I fired my endo.