I have one of the first gen (short magwell) receivers. All mags pitch back & forth a little, but it doesn't affect reliability...
Mine isn't finicky at all. If the mag works in my ARs, it'll work in my '17, and all will drop free.
For prone / sighting in, I use a 20. Otherwise, I keep a 30 loaded for unsocial occasions.
I'm saving my pennies to get a C-Mag...(twitch-twitch, *maniacal snicker*