I am a rifle enthusiast so I keep several around. I never have to settle for just one rifle to apply to all types of hunting.
6MM Rem, 700 BDL, for deer and the occassional fox or coyote. Works great for knocking the heads off late season pheasants in the stubble.
260 Rem, 700 ADL Titanium for above the treeline. Not a super light weight, but it tops out at 6 pounds with scope, mounts, sling and 4 rounds. Thanks for parting with it A-Zone.
270 Husky. Not my favourite rifle, but I like having a rifle for which I can buy ammo at any gunshop, Canadian Tite or Wal-Mart if I am in a pinch.
280 Rem on a Titanium 700. My custom build and go-to gun for everything. A bit heavier than the original Titanium, but a lethal long range rifle in a lighter than average package. If I could only have one rifle for all types of hunting, this would be it.
30-30, Model 94. Great 100 metre or less bush gun. Ammo available anywhere.
35 Whelen. Great medium bore. Low recoil, big punch. Primarily my moose, elk and bear rifle, although I have yet to take a bear with it. I also carry it for deer in the thick bush as it anchors them on the spot every time. My #2 choice if I had only one rifle.
If you want only one, general purpose rifle, there are a hundred or more threads on which to choose.