What is the difference between Japanese and American parts?
In short, Japanese parts tend to be more sensitive and responsive. American parts typically require more effort to move and engage button commands. People generally view Japanese parts to be of higher build quality. That doesn’t mean they are necessarily “better.” Most of the top Japanese and American players use Japanese arcade parts.
On top of that, these days pretty much all of the commercially available off-the-shelf arcade sticks use Japanese arcade hardware, so they are easier to find.
What is the difference between Sanwa, Seimitsu, and other manufacturers?
Sanwa and Seimitsu are the two largest producers of Japanese arcade hardware. Which should you get? Ideally, try both out and decide which you prefer. If that isn’t an option for you, just get a stick with Sanwa parts. The Madcatz TE stick is full Sanwa stick and buttons and most of the Hori Real Arcade Pro (HRAP) line has a Sanwa stick at minimum. Seimitsu parts also have a lot of fans, but really, you can’t go wrong with Sanwa.
As far as American parts go, ironically the best American parts currently come from a European company, “iL.” If you’d like to know more about Sanwa, Seimitsu, and the other arcade part companies, consult the essentials thread.