I shoot a .270 Win, my dad shoots a .30-06. The .270 shoots flatter, which is a plus if you're shooting at longer distances. .30-06 usually has a larger bullet, which can give you more knockdown power.
Both get the job done. The deer don't seem to mind what hits them.
While we're on the subject of cartridges, does anyone have any opinions on the 7mm Rem Mag?