Well if you go off the beaten path, you will find 243, 270,308, 30-06, 7mm Remington Mag, 300 Winchester and 338 Winchester, along with 223's and 22RF. That is pretty much common in America. Now what is best, gee's it become another tastes great less filling debate. Common sense for most would be a 308 or 30-06 for reasons that most can shoot them well, 300 or 338 are about as good as it gets, but with them comes both recoil and weight, I like the 338 for most all of my big game hunting, Elk mostly, I when Black bear hunting once or twice and same for brown bear. As for polar, well I can't afford that. I have in the last few years gone back to the 7mm Remington Mag. I shot one back in the early 1970's. But when its all said and done, you would be hard pressed to do better with a .30-06. For most of what North America has to offer game wise, and this is from a fellow that shot a lot of game in NA with all kinds of rifles and cartridges, and I for some reason never warmed to a 30-06, when common sense tells me, its really the way to go.