I just bought a pair of Lancer L5 mags. After loading them up and trying them out on the range, in my gear bag, in my mag pouches, I have to say they hold up to PMags in both aesthetics, form, and function. BUT WITHOUT some scientific & material properties testing, I can't say who'se is the better mag - but then again, since these have both been around and been tested by 1000's in the industry with great results...
It all comes down to personal preference. BOTH ARE EXCELLENT TOP-OF-THE-LINE POLYMER MAGS, as far as polymer mags go.
I can say however I won't be buying too many more Lancers. Don't get me wrong - I really like them a LOT. But...I have a boatload of genuine US Military Surplus USGI MOLLE II M4 Dual Magazine Pouches, and a boatload of MOLLE I/II gear (LBV vests, MOLLE packs, etc). Standard 30rd aluminum USGI's & PMags fit those US Mil-Surplus dual mag pouches perfectly, with the USGI Aluminum's being the easiest. The Lancers will fit, but the prominent plastic ribbing on the outside of the Lancers make it damn near difficult to insert and slide in, and might more likely rip up any fabric of most any MOLLE mag pouch.
Obviously, "mag-pouch-fit" shouldn't be the criteria for choosing the Lancer vs the PMag or some other polymer mag. But I've already gotta helluva investment in USGI mag pouches and MOLLE gear. So for me, the PMag wins as far as polymer mags go - plus the PMag and USGI's are notably a lot less $$$ than Lancers nowadays.