I'll give you a legit reply but I can't say this is 100% accurate. This is based on personal experience and what I read on here.
Korean-These girl do plastic surgery. They tend to lean towards their 30s. Lately they've been pushed out of the city. There's still some OGs out there, you'll have to ask around. As for sex, decent out of the three. The OGs however will rock your world. Unfortunately they may not be the best bang for your buck nowadays. Still, there's a few good one's out there.
Chinese-They do more for less. They tend to be much older out the group. There are plenty of young ones though. You can't trust a C-girl's photos. Chinese girls in my experience tend to perform really well. I've had some rapport with a few, so maybe easier to get along with. I believe the quality of the c-girls have been slipping as of late. Probably more good reviews of Chinese women on here than any of the group. There are a lot of GOATs in this community.
Japanese-They started coming here around 2021. This was after lockdown when a lot countries were still not open for tourist. The US opened up and J-girls needed their money. They made a killing here and it opened the floodgates. The girls here make way more than they do in Japan. Even JAV girls make more money in AMPs than JAV. So now they're pretty common. They legitimately changed the game once they got here. J-girls tend to cost more than Korean and Chinese girls. Every so often a few might popup that's not too expensive. J-girl tend to be in their 20's and a few in their 30's. They're more willing to do extras than most. In fact, their willingness to do extras changed the landscape of the business. Hell, I even partly blame them for increasing prices. As for the sex itself, it varies of course. There are a few stand-outs who pop up every once in while. You have to keep a look out. Some problems I've read and experience once, J-girls may sometimes block you or need time to adjust. Japanese girls alo legit do JAV moans/scream. It can get annoying after a while. As for sex it can go either way tbh. It'll either be really good or really bad. Japanese girls are very polite and service oriented. Although that's not the case for all of them.
Once again, these are just my observations. If you think I'm wrong or right, chime in.