7 mag if forced. This months shooting times has a good article on that.
Between the two you offer, toss up really. I'd ask the size of the game for one. They're pretty close, but the .30-06 has the edge on really BIG game just because it can shoot heavier, better bullets for big game. Get inside 300 yards up to elk in size and just pick one. The .270 is easy on the shoulder if that matters. On deer, I'd go with the .270 at long range. But, the range advantage won't be that big a deal IMHO.
And, yeah, lots of variables like the bullet matter. The .270 does tend to shoot a little flatter in general, though. The difference ain't enough for me to waste ink writing home about, though.