My research indicates Hainan Airlines probably has the best business class product, Air China maybe second.

Looking at SEA-PVG and PEK-SEA and plan to get to SEA from LAS with miles from various airline options. However, I cannot get the Hainan website to function. I can put in my desired booking but when searching for results it comes back with an error message. Occasionally I have gotten it to show flight options on the way over but after picking one and trying to view the return options I get that same error message.

Hard to see how a major airline expects travelers to book with a website that does not function.