If you are going to hunt for larger game buy a .308 and shoot the lighter rounds when hunting deer and the 180 gr Ballistic Silvertip stuff when hunting game slightly larger than deer.
If this is your plan, get a .30-06, which will give you a couple hundred FPS over a .308 with a heavy bullet. The .30-06 is identical in size to the .270 -- it uses the same brass, but with a different neck diameter. A .308 only makes sense if you really need/want a short-action rifle, or if the gun only comes in .308.