If I could only have one big game rifle it would probably be a .300 either in Win or Weatherby. Its big enough for elk or moose and small enough for deer, sheep and antelope. Flat shooting enough to be able to hold dead on to a decent distance and heavy enough for long range.
I think the .300 WSM deserves more consideration. It has fantastic ballistics and is very capable of kill shots on most North American game, as well as most African plains game. Many rifle makers offer a .300 WSM in a fairly lightweight rifle which is great for hunting in the mountains as well. One rifle, the .300 WSM gets my vote.
Had the 7mmSTW, it was superb, but this time I want to step up the game, so its the .338 Lapua for me with 300 grainers....Shocking knock down power at extended ranges is what i want for those New zealand Chamios and Thar.my son Robbie uses the .300WSM for great results to date.