This year I have used all the three appoaches to communicate with IRS for my (our joint) federal income tax matter. Things have been mostly resolved now. But looking back I think I could use the IRS local office more often. Each appoach has its pros and cons, here are my takes on each appoach.
Probablly the slowest. But it is also prudent. By “prudent” I mean it usually takes couple rounds of back and forth to get things right, I learned the mistakes along the way, but eventually I got it right and they got it right too. One needs a lot of patience though as I suspect IRS service centers are swamped by the stimulus checks this year.
I heard it very difficult to dial in. Luckily I got handfree headset so I tried: one failure, one success. I was just querying one thing, and they gave me an answer.