So would anyone today, in 2020, put China in the number one spot? (I wouldn’t, fwiw, but I wonder if any here would.)
For me, at least, there's more than just number and/or quality of the creds themselves. There's a faff factor which wraps up everything associated with travelling, spites, etc.
Now, I don't profess to be any sort of expert on travelling in China - I've only done it once - but I'm sure most would agree that the "faff factor" in China is much higher. Looking at it from someone in the UK - you've got visas and language barriers to contend with, as well as the cultural stuff that we're unfamiliar with. I like to to think I'm pretty adventurous (or at least, open-minded) to getting stuck in, but there's definitely cultural shocks to adjust to in China - food being a good example. Sure, I had KFC and Pizza Hut a few times while I was there, but I also did try to eat mostly at 'non-Western' places which wasn't easy at times. If you can't read a word of the menu (and not just kinda breeze your way through it like you can in most of Europe) then you do have to be a bit brave. Now I have [medically mandated] dietary requirements, I'm not so sure how well I'd get on, to be honest. Checking something with the hotel front desk, quickly scoping out a route on the map, they're all slightly harder.
We're all different though, and no doubt someone else will have different perspectives.
That's a digression, possibly, but all of that is to say that travelling around the USA is
SO EASY for Europeans (arguably the easiest, as you've got one common language across the whole country - albeit with different quality levels!) that doing a coaster trip there is simply more straightforward. I've done most of the major stuff in the USA now, and only a tiny handful of China, but where would I rather spend three weeks on a coaster trip right now...? Not as clear cut as creds alone.
China could easily sit in the top three, but I'd probably place it behind USA and Europe (grouping that up as it only seems fair from a scale perspective) for the 'convenience' factor.