Nine pages devoted to this question? C'mon .. .308 and .30-06 .. almost no difference.
Yes, the .30-06 has a longer casing and can hold more powder giving a slight advantage in terms of muzzle velocity and energy.
But does that translate into either being a more effective tool, either hunting or at the range? No.
Now, if you had asked about the .270 vs either .308 or .30-06 .. then you would have significant differences to discuss.
the .270 is really a 7mm-06 .. providing the shooter with a more effective SD, flatter trajectory, excellent accuracy and superb downrange killing power.
But hey, this wasn't part of the question, so I'll just not mention it.
=)