In my two "AR10" 's - M&P 10 and an Aero M5, I'm using Magpul's. Am no expert they are both recently purchased.
Magpul does make 3 models of these as far as dimensions - one standard, one short action, and one for ammo that is longer than spec. I run the standard.
Personally if I am gonna shoulder the rifle I prefer the 25 round models - +5 rounds is not much weight or space compared to AR10's which are heavy. If I am going to use a rest then I like the 10 round models, fits better under a bipod... I also like to under-load my mags, using a 10% rule, to keep from squishing the springs - a real concern? not sure, but at least if I'm storing them loaded I put 22 rounds in a 25 round mag, 36 rounds in my 40's, etc.. etc..
I do have some 20's, nothing wrong with them, but what I'll stock up on are 25's and will keep a handful of 10's around for precision stuff.
As far as metal versus plastic mags - personally I'd rather drop a rifle, or put some odd pressure on a mag, or god forbid if I kaboom a rifle, and have the mag be the weak link that is destroyed. I will not run metal mags, got a few, they live in the misc gun parts box - no use for them. Mags can be plentiful compared to a rifle or your safety - a mag being the weak link is the better design.
On a regular basis I pile a duffel bag full of magpul mags of various types (ie like up to 500 rounds worth in a single bag even) and I lug them down the stairs, over the doggie gates, out the front door, into the truck, plopping the bag on the floor here and there as I go, then onto the hood or on the ground, occasionally even dropping the bag or tripping on it - no failures. Pmags are good.