So far as rarest, the P220 9mm With all the American button is, IMHO, the rarest. I have many with the ecu launch, but haven't witnessed 1 in person Using the American button. The P220 and the remainder of the P220 series of pistols are legendary for their strong building https://sigsauerp220forsale37147.amoblog.com/sig-sauer-p220-for-sale-can-be-fun-for-anyone-48767751