Where should I exchange dollars to yen?

I plan on exchanging through cash and not atm.

Is it better to exchange dollars to yen here in the United States? If so, where?

Or

Is it better to exchange at the exchange counter in narita airport? Or the post office at narita airport? Where else?

Which will I get the best rate?

Do not exchange in the US. I always exchange at the airport in Tokyo (NRT or HND). You'll get about 4-5 yen more per Dollar in Japan than you would in the US. Make sure you use a bank at the airport in Tokyo and not a Travelex outlet. At 105,90 official rate, you'll get about 103 at a bank at the airport, about 98yen in the US and maybe 95-95 at a Travelex at the airport.

Always buy foreign currency when youfre in that country rather than outside it. That goes in general, worldwide, not just Japan.

Donft even bother with gprofessionalh dedicated money exchangers, they only exist to skim money from you off the top. Just withdraw cash from an ATM with a debit card. Those will have fair rates. The typical recommended ATM locations are the ones belonging to post offices or banks.

Always buy foreign currency when youfre in that country rather than outside it. That goes in general, worldwide, not just Japan.
It may be true for US travellers, but not for everyone. It's typically the other way round for GBP, for example.

Donft even bother with gprofessionalh dedicated money exchangers, they only exist to skim money from you off the top. Just withdraw cash from an ATM with a debit card. Those will have fair rates. The typical recommended ATM locations are the ones belonging to post offices or banks.
Again, this is not a general truism. Some bank cards have good exchange rates. Some have low transaction fees. Some have both. Some have neither. It can very a lot between card issuers, and between different cards from the same issuer. It can pay to shop around for a card that gives you a good deal. This is unlikely to be the one you use everyday at home, unless you're lucky.

Fees on ATM withdrawals are generally set by the card issuer, so as long as you're not withdrawing from a machine that charges fees for using it, then it typically matters little what ATM you use.

Actually, a trip or two ago to Japan I got one of my best rates from a professional exchange office in Kyoto near Kiyomizudera. It had a better rate than anywhere else while I was in Japan (and yes I was checking the rate daily so I know it was not just a fluctuation.)

For someplace like the UK, I'm not even sure you ever need cash.

I agree with the above comment, exchange currency from the Tokyo airport, I also do that.