I own both calibers and for Gumby's intentions the .270 is a better choice. I drop deer all the time with my .270 long rifle and my .308 handgun. The .270 is every bit as efficient with less meat loss. As far as ballistics, it out performs the .308 at long range as well.
.270 Swift Sirrocco 130gr, 1211ftlbs of energy, -38.2 (drop) at 500yds
.308 Swift Sirrocco 150gr, 1156ftlbs of energy, -46.0 (drop) at 500yds