I've used Pmags, Hk SA80, USGI (issued Colts, and others) some w/green followers or Magpul followers, and 20 round Colt (old USGI) in my XCR. My other mags experiences, all other brands of USGI aluminum mags, Thermold, and orlite. Avoid Thermold (any generations) and Orlites!!!
All these mags work great in the XCR as they do in any AR. Only on "the net" is where I hear about other brands of AR's having problems w/mags, but I only have used Colt's and a few times FN made M16's and my basic training and first duty station original M16A1 made by GM Hydramatic Division.
For a rifle as tough as the XCR is I recommend Pmags and Hk mags. Both mags are tough although pmags have had some initial production issuesl. I like them both. The Hk ones are very smooth and I'd rate them #1 in reliability, pmags #1 in toughness and best value.
USGI mags all now exclusively come w/the "less" tilt green followers instead of the old black "often" tilt followers. They are reliable. The magpul "no-tilt" (and I really mean no tilt!) followers make the USGI mags about as reliable as they are going to get.
One of the AR/M16 weakness has been the mags, particularly the followers tilting b/c of debris or most commonly the mag body getting dented or deformed, followed by the mag lips getting the same treatment. You'd step on one accidentaly and then wouldn't work w/o noticing any damage on the mag. Now all the AR cool-aid drinkers who swear that the AR is uber reliable had missed those dark days of the crappy mags. Pretty much since it's inseption up until the mid 90's when the green followers came out AFTER the Gulf War and Somalia, both of which I went to.
Unless you plan on running them over with your truck the original USGI aluminum mags will be fine, but as I said the pmags and Hk mags are best. We ran the almost exact same tests and managed to break them both the Hk and Pmags after the 6th or 7th run under a fully loaded Tahoe on a hard packed and gravel strewn dirt road. I'm sure if there were a fire test the Hk mags would win, BUT at $15 bucks a pop and still as tough, if not tougher, the Pmags are the shizzle. You'll get 2 Pmags for the price of one Hk SA80 and still have money left over to get a few Gatorade's.
Historically plastic mags have always sucked. Looks as if the Pmags will be the exception.
And no, I don't work for Magpul, but both MP president and I were in the Gulf War, so I know where he had his experience.