"06",
I have to agree with Rimefire, we need more info to answer your question.
Most people don't want to pack a 17+lb rifle in the mountains (I do) so if that is your use the 338 AM may not be your ticket...... However, if sending a 300 SMK down range as fast and flat as possible, the AM is the way to go.
I have a 338 rum, 338 edge, 338 win mag, and 2 338 Kahn's (338/378 improved). As a general rule I find myself reaching for one of the Kahns when I start planning a hunt. I suspect if I had a 338AM that is what I would be carrying. I just like the big guns and don't mind packing the weight.
If I had it to do all over again, and just wanted 1 moderate weight rifle (12-15lbs unscoped) I would probably go with the 338 Lapua. Great brass, a very accurate round, no fireforming....... similar performance as the Edge. Go with AI version and you have the best performance without going all the way to the 338AM. Obviously my opinion! Everyone has one!
With your limited information, a short answer would be 338 Lapua for a light(er) weight rifle or the 338 Allen Mag if you want to go for the best, most high power thing out there. Either way, get Kirby, (Fiftydiriver) to build it for you, you won't be sorry!