All of them are known well. However I seem to have missed out on Quinpu !
Wouldn't you need to listen to them before buying ?
Of the lot Quinpu is cheaper than the rest. Shanling spends a lot of money on solid aluminum decorative chassis. I think you pay more for the casing.
Yaquin appears more classical in appearance and so must be focusing on sound. By looks I'd pick Yaquin first for a test as they spend much less on the casing and so possibly may produce better sound. They are expensive . However you might get their local version with different Chinese names at a much lower price ! You might need to ask a local hi-fi fan !
Why visit a Chinese Tube amp factory ? Just to buy a tube amp ? You can learn everything about building a tube amp from Morgan Jones's book ! What no company will teach you is how to wind the output transformer. Each one has his or her own method which is their trade secret ! However all the basic principles are all there for free on the Net !
If you want a really good 'reliable' tube amp , you should just buy tubes from China with a good output transformer and build it yourself ! A good tube amp can weigh a ton !
There is no 'best tube amp' ! Not even in the West ! Each has it's own idiosyncrasies . You pick what sounds best to you !
I'm guessing you are not a billionaire in which case you could buy a whole lot of them and declare one IS the best ! But then it cuts out a lot of fun !
Enjoy your trip !