I'd pick the .270 WSM of those two. But I also will second the .257 Wby. Mine will be here tomorrow if UPS does their part!
To be honest, the 257 Wby is probably a little light for an elk cartridge. However, if I were hunting out west for mulies, and I also just HAPPENED to have a cow elk tag in my pocket and the 257 Wby in my hands, and a nice cow elk stepped out at less than 300 yards, well... I'm not going to think twice about drilling a hole in her boiler room with a 115 grain Barnes TSX, as long as the shot's good. I'll bet she dies just as fast as she would have with a 180 grain .30-06. If I were going elk hunting with a bull tag with elk being my "primary target," I'd probably pack the .30-06 with the 257 Wby as my backup rifle.
Mike