Not like I'm biased or anything but i say if you've got to have polymer then you should go with the people who invented the poly frame handgun...
HK.
Oh, and by the way did I mention I own a few: USP45 Tactical, USP45, USPc45, USPc40/.357sig, P7M8x2. The HK collection has ballooned in the last few years because they are the only guns in my collection that are dead nuts accurate AND reliable. Glocks, owned two glad to be rid of them. Own a Sig226, nice gun but I still prefer my USP's. And did I mention that I just got back from a three day defensive pistol class. Anyone wanna guess which manufacturer made the only two guns that went belly up during the entire class? Starts with a "G" and rhymes with ROCK. Which by the way they have a lot in common with, at least after three days full of sand and dirt they're just as dangerous as one. Heck, even the "custom" 1911 survived unblemished. My USP45 had one type 1 malfunction due to dirty training rounds (snap cap).