Like Superpig said, it doesn't take a magnum to kill a hog. I've killed a bunch this year with some handloads from my .223. Pop them in the head and they'll go down.

Of the three, my choice would be the .270. Nice, flat shooting caliber with out a lot of recoil, and a wide selection of ammo available almost anywhere. Plenty of gun for a hog or a deer.