Master links are garbage. Get a chain checker and you'll see that they start stretching at the master link in about 1000 miles or less. By the time you start seeing the stretch at the master link, it is already stretching minutely at the other links of the chain because of the initial stretch at the master link. I have documented this with my lbs and they agree with my findings after checking it out with several other bikes they have had in for repair. The pins are the way to go for chain and drivetrain longevity.
This is with the KMC links, not sure of other brands. I no longer use KMC and only use Shimano. My chains are lasting 3 times as long now.