OKEx doesn't allow US customers. Even to be able to withdraw $1,000 per day you would need to use VPN and provide a fake name/passport number. US traders are better off staying on Binance and using VPN. Only email address is required for much higher withdrawal limits.

Houbi banned US customers on its international site. They have a US-facing site but it's only got ~ a dozen coins listed.

So if you want to be "legit" then Kucoin is the best option. If you're willing to VPN from the US and risk the consequences, Binance is still the best.