ORIGINAL: Gut Check
I would say 30-06 if you own one gun. I don't own one but I do own a .270. There is absolutely nothing wrong with the .270, in fact, it is my favorite deer rifle. If you are looking to go elk hunting or other bigger game animal then the 30-06 gives you better options for a larger round. I know that alot of people would argue that a .270 is adequate for elk but it is below my comfort level. I had an Encore for muzzleloading and ended up buying a .300 Win Mag to go elk hunting for the first time this year. If budget isn't an option, then buy them all!!!
I've taken 3 moose with a .270...So elk wouldn't be a problem. Mind you it is under my preference, its the only Rifle I have, and has taken 3 nice moose, and all have fallen within 100yrds of being shot, 2 didn't even make it 30 yrds. But When I have the extra cash I want to pick up a .300 Ultra mag or .338 mag.
I voted .270, because I have one, and love the caliber. Its a very flat shooting gun, and plenty of knock down power for deer. If you did think you may hunt bigger game the .06 is the better choice because of ammo selection, but for strictly deer, its a great, flat shooting Caliber, with low recoil, and very accurate.