I have a Remington 700 SPS Tactical in .308, with the 20" heavy barrel. This rifle is bad ass! I can print 1/2 to one inch groups at 100 yards all day long.
Since my rifle weighs about 9.5 lbs with the bipod and scope, the recoil is nothing, about like shooting a 30/30. No flinch = accuracy! I can put 30 rounds out of this rifle without even blinking, very easy on the shoulder.
The 300 win mag in a standard sporter rifle will have brutal recoil, pretty close to 30 ft lbs. The ammo will cost you double and the barrel life is less than half of the .308. According to recoil calculators that I have used, my .308 has about 14 ft lbs or recoil.
I reload 168 grain HPBT's for about 45 cents/round.
My vote......308 Winchester!