There can be only one...
Not many people can say they are famous for making a switch. Don is (actually) famous for his amazing flashlights, but his switch is equally well known in the flashlight world. Accept no substitutes. When other switches fail, they get replaced with a McClicky.
This is a "forward" type clicky, which means it allows momentary activation when the light is in the "off" position. This switch is very robust and has a much better electrical path than any other switch I have disassembled. The intermals are beefy and have large contact areas compared to other switches. This is especially important in high-current applications.
This switch sets the gold standard, but you can expect all mechanical switches to fail. That's what happens to things that have moving parts. This is the best switch on the market, but it won't stop it from wearing out. Might as well get a hand full to keep on hand. Remember, two is one and one is none.