There is no "one gun" I can pick, there are several that I always find myself turning too, even though I have three packed safes.
For small game hunting, its my Kimber bolt .22 with a 2x7 scope. The gun looks good, handles good, and shoots like a target rifle. Almost feels like cheating when I take it into the woods.
Big game, its a tough choice, but I would say my early model Browning BLR in .358 win. with a 1.75X5 scope. I can load it with cast slugs at 1200 fps for plinking or small game, or 250 grain Noslers at 2300 fps for about anything that walks. I have lost track how many deer this rifle has killed, along with several hogs, black bear, one moose, and a few dozen grouse for the pot.
Varmint would be my CZ .204 Ruger with the Nikon 4.5x14 scope. Even though I have only owned it about a year, it has quickly become a favorite. Pretty wood, great trigger, and so accurate, it stands right with my heavy barrel 22/250's, at about 4 pounds less weight.
Behind the seat in my truck? A Bushmaster semi auto M4 with a Burris 2x7, a Burris Fastfire holo sight, and a Streamlight TLR 1 flashlite, along with 5 30 round mags of assorted ammo. Never jams, and is way too accurate for what it is.
So, these four, I would say...
Larry