SIG Switzerland, the original who mainly services the Swiss government and domestic market. They created the original P210, SG 550 series, etc
SIG Sauer Germany, the now-defunct company SIG Switzerland created when it bought German firearms company JP Sauer and Sons in order to develop, market, and sell firearms in a legally easier jurisdiction. They are most famous for the P220 series of handguns.
SIG Sauer USA, the New Hampshire based company that was initially created to make importing easier that is now by far the largest and most well known SIG. They created the P250, P320, P365, SG556, MCX series, etc. They are very well
Overall, SIG Switzerland and Germany have very good reputations for making high quality products (Sig Sauer Germany almost won the competition with the P226 to become the M9, they lost because they were more expensive than the Beretta 92, very similar to what happened between Glock and Sig Sauer USA for the M17...), SIG USA on the other hand does not.