We'd need to develop some metrics here. If you're defining an A rating as meaning you never encounter DCC or are at least proactively offered a choice beforehand such that you never see receipts with DCC verbiage, then I would say Taiwan has about a B- rating. I say this because most places will offer a choice or give you the quote slip and then respect the choice, but there are other locations where you have to watch the cashiers like a hawk to make sure they actually follow through with the DCC opt-out. What helped the situation in Taiwan is that Visa cracked down on the DCC practices here, so now terminals are much more compliant. In terms of ratings when encountering DCC:

Ratings:
A+: No DCC at all
A: Clear and conscious choice provided upfront with markup disclosed over Visa rate; you never see a slip with DCC verbiage because the cashier disables DCC for the transaction
A-: DCC present with choice given but cashier makes no attempt to explain the choices or point out the markup; choice is always respected, however

B: DCC is selected by default and DCC amount is held as the pending transaction; markup disclosed in the fine print of the DCC verbiage on the receipt; quote slip is usually given; DCC choice is almost always honored, at least for those in the know; people unaware of DCC or those who don't specifically opt out or request local currency will get hit

C: Requires a proactive stance against DCC to avoid getting hit; merchants will almost always be able to accommodate a customer's request to be billed in local currency provided the customer requests (or is adamant) about the request upfront; can usually avoid DCC as long as you're extremely vigilant

D: Getting into forced DCC territory; some POS terminals automatically opt in to DCC without a straightforward way to disable it, such as Burger King in Ireland or coffee shops in Eastern Europe. Most chain hotels will claim there is no way to disable it either. You often see merchants coercing customers into accepting DCC making it seem like the end of the world if they don't accept and saying things like "Good choice!" when accepting DCC.

F: Even the advice on this thread cannot help you here. Unless you want an uphill battle and your significant other and friends are patient enough to wait while you argue for 20 minutes with the cashier over $2.35 DCC charges on principle, just take the person's advice and "Use UnionPay la ".

See advice for grade F geographies.