Well if you mean a 7mm mag vs a 30-06 then the 30-06 will have a little bigger frontal area as its a 30 cal and the 7mm is .284 cal. With a bullet of equal weight the 7mm is going to have a little flatter trajectory and a little more energy due to the higher velocity. The 7mm bullet will have a little better sectional density. The 7 mm will have about 2 more ft lbs of recoil when fired with an equal weight bullet. Both are common calibers and cartridges should be available for both anywhere that sells ammo but the 30-06 probably gets the edge in availability. You will probably also find the 30-06 offered in more bullet types and weight variations. Both would be well suited for virtually any North American big game animal with the possible exception of the truely large bears like the big Browns or Polar bears.

In pure performance stats the 7mm out does the 30-06 but kicks a little more to do it. However the differences aren't that huge if you compare them on a ballistics table. You can't go wrong with either one. Both are great calibers.