polymer as it is lighter, last longer, absorbs recoil better than wood and more resistant to weather and chemicals
I disagree with this statement regarding recoil. My poly stock 30-06 kicks like a mule. My buddy's wood stock 30-06 is much more fun to shoot because it does not beat the hell outta my shoulder.
I generally like wood better for aesthetic reasons and recoil. The exception is 22 rifles (no real recoil). Love my super light Marlin 795. I think it comes in at less then 4 pounds and is accurate as all get-out inside 150 yards with high quality ammo. Heck, it's still generally a great shooter with the cheap stuff too