I have Lancer 20 rounders, Magpul 20's and D&H 20's. They all work in my AR's. I don't have a preference and buy whichever of the 3 is cheaper when I need to add to the stash.
Can't remember paying more than $11. bucks a mag, for any of them. I also have a couple of 10 rounders (Lancer) that I use only for load development.
And yes, I have way more 20 rounders, than 30 rounders. I like prone shooting off a bipod or my pack; keeping my pumpkin down; and besides I'm too damn old to run and gun any more.