Steve, while a .25-06 is a fine deer killer it does suffer from some deficiencies when compared to a .260 - especially for those of us who like a shorter barrel while sitting in the tree stand. First, the .25-06 is a relatively inefficient powder burner. It requires a pretty long barrel to get its velocity. A .260 slows down relatively little until you drop below an 18" barrel. Second, if you do use a short barrel on a .25-06 you really pay for it with muzzle blast. That is not the case with a .260. Third, the .260 is capable of using a heavier bullet. A 120 grn bullet is heavy for a .25-06 while a .260 commonly comes loaded with 140s and handloaders go even higher than that.
Those 3 characteristics mean that the .260 makes a more "usable" deer rifle for my needs. Now, if I lived in a different part of the country and had different needs then I may very well choose the .25-06.