Is the 25-06 better than the 270? Not a chance if you are talking about big game hunting. The 25-06 is a great round but the 270 takes your options a step further because it has heavier bullets available. The 280 take you another step with a bit heavier bullets yet. They are all the 30-06 case so it's all in what weight bullet fits your hunting needs. I like the 25-06 better when I may do more varmit hunting than deer hunting although its great for deer. If it's mostly deer and bigger then the 270/280 would be my choice. For deer with a rifle, I like a bullet with a SD of 200-250 with about 220 suitung me best. I always pick my bullet by what I need it to do then see what cartridge will deliver. The more options one rifle will fill just makes selection more simple.

SD is not everything but its a heck of a guide line. If you look at a caliber that has a good selection of well constructed bullet, say the Nosler Partition, the higher the SD of the partition bullet, the more penetration you will get. A happy medium is needed though because a bullet with to high a SD may not expand much if at all on medium game.