Meprolight and Trijicon are the 2 big names but there are others. I have used both and really find little difference in them. Both are bright, have 10 yr or better warranties, and seem to stand behind their products. I have heard that Kahr Arms (the moonies) bought Meprolight so if you have a personal reason against that, it kind of narrows it down.
IWI (PT) makes some that offer different color inserts for front and rear, along with dots or bars on the back. I like the idea of different colors but in checking them, the green always seems to be the brightest. The yellow doesn't look much different than the green. The orange or red are not quite bright enough to me to stand out as the front sight. So in reality, the rear green seems to dominate the other colors of the front sight, unless it is green too. Now you are back to having them all green.
Heinie offers a version of his Straight Eight that is an option too. I really like his regular sights but not sure the dot over dot arrangement of the Straight Eight would interest me.
Ashley (AO) offers a tritium sight in their large front dot-rear V shaped Express sight with a bar. It would be very fast close up but like the rest of the AO line, more difficult to be precise at distance.
Novak sights are available with tritium too, if you like the lower no-snag profile of them.
If you want adjustable sights, Meprolight and Millett offer models for the SIG.
And Enterprise Arms offers a Ghost Ring night sight version.
You have several choices. It depends on what you want it for.
If it was strickly for CCW or a home defense gun, I might lean toward the big and bright Ashley. Use here would probably be very close and fast.
If the gun was also used for competition or target work, the target blade design of the Heinie would offer an excellent sight picture for daylight shooting too.
For CCW, duty, or all around use, I would probably just stick with the more standard profiles of the Meprolights, Trijicons, Novaks or IWI designs.
I don't see a need for the adjustables or the ghost rings.
