If I could only have one, period, then the .260 would allow me to load down for varmints; the .22-250 would not really let me load up for large, thin-skinned game; the .243 is a nice round, but would still have an upper limit.
Not that the .260 is a powerhouse, but of the three, I'd go with it, as it would offer the most versatility.
Now, of those you've listed, if I were going to add to my current collection it would be the .243, as I have nothing in that category. I already have rifles in .30-06 and 7mmRM, so I don't really need a .260 for larger game.
And if you asked what I actually think I'll get next, that would be a 6.8SPC upper for my AR.