That's a little tough to answer. If i could only have one bullet for everything I guess it would be the only bullet that is left.
That is pretty tongue in cheek. I know what you are saying, you want to simplify. I have been there as well. The more that I reload and tinker, the more different stuff I seem to need.
When I only had a 30-06, I had one load. I shot a 180g Ballistic tip. Able to shoot anything on the the North American continent within reasonable distance. I have ammo cans full of it if I ever have to dig into the reserves.