Years ago, I got the advise that when choosing a big game cartridge for North America, the minimum configuration should be a 120 gr .257" bullet fired from a rifle-cartridge combination that will keep the bullet in excess of 2000 fps at the target. The .25/06 seems to do this in spades. My experience has caused me to revise the minimum criteria to 6.5, but this does not alter the fact that 95% of the time the .25/06 will get the job done.
The .270 has some advantages that cannot be overlooked, but it is up to the individual hunter to know if those advantages are an advantage to him. The .270's velocity is less effected by choosing a shorter barrel than is the .25/06 velocity. This means that the rifle can be shorter, lighter, and handier with a smaller sacrifice in performance. Heavier bullets are available for the .270, but unless you are an elk, moose, or big bear hunter this is of little consequence, and the .25/06 kills moose. The real advantage here in favor of the .270 is that a short barreled rifle looses less velocity in comparison to the long barreled rifle when loaded with heavier bullets. This is because the velocity is initially lower with heavy bullets and there is less powder to burn under the heavier bullet. It could be argued that the .25/06 will have a shorter bore life, but this argument is flawed on a number of levels since there is an overlap of bullet weights and powder charges between the two cartridges.
When the game is a Dall sheep, pronghorn antelope, caribou, or other difficult to reach game, a long barreled .25/06 would be hard to beat. If the list of game is going to include animals that exceed 1000 pounds, or game hunted in difficult country, a compact .270 might be the better choice.