In my experience, Wilson Combat is regarded as making the best 1911 magazine.Who makes the best and why? I like Wison Combats. I think the hold up best.
I was basing my opinion on the STI mags from shooters reports. He has had good luck with his. They appear to be decent, but experience trumps appearence.I think Checkmate is what Ed Brown's come with. The mags STI's come with are less than stellar. We've had a lot of issues with them especially in the 9mm where they feed to low into the ramp and fail to feed. Swap them with another brand and the problem goes away. Its not a lip issue either, been there, messed with it several times