If I had to choose one, it would be the '06. It can be used in a wee bit more situations. Both are good deer rilfes, but the '06 is a very good (though probably not the best) elk rifle. Probbaly better than the 270 on elk mainly because you have a better selection of heavier bullets like 180 grain. If you head out to the deer woods and forget you ammo, the gas station at podunk Oklahoma is more likely to have 30 '06 and 30 30 than any other cartridge.
If you reload, there are more components for the '06 and 30 cals than any other.
But the 270 is a dandy round and is such a classic western cartridge because it may shoot a tad flatter than the '06. Jack O'conner took alot of Elk, Sheep, and Muleys with the 270 out west. You could do alot worse than follow in Jacks footsteps.
Go to your local gun store and price a basic box of each. Maybe that will help. I think '06 is about the cheapest big game ammo out there.
But you should get one of each!!!!
okcmco