Have to say at the moment .308 simply because I grew up with it and its what most my longarms are chambered in. Have been looking at .260 and .280 lately as well, but haven't got past the farting around with them stages.
The old 06 is hard to beat, yes the big magmums will kill farther,but get meat on both ends, I suspect That I will hunt nothing bigger than Elk and the old 06 will do the job, a lot further away than most hunters can hit what they are aiming at. Most of my shooting is with obsolite military surplus rifles a Garand 03 a3 Springfield,Mauser M/N and a K31.
I'll Stick to my mention of the '06 family, but if we're talking short guns, I'm a 45ACP man myself, but the 44 Rem Mag does one hell of a job on whatever you point it at.