re: .308 vs .270

Any modern centerfire cartridge will easily take deer at the distances you said.

Of those two it's really up to you.

For me, it would be the .308.
the .308 offers probably the biggest range of available loadings of any cartridge.

You can load 110gr for varmint hunting all the up to 220gr subsonics for use with a silencer to get stupid quiet.

I have 3 (though I will be changing calibers on one of those)

Now that I think about it, I have an extra AR barrel in .308 sitting in my closet.