I have a .260 heavy gun and a 6.5x47 light gun. I like both for what they are, and wouldn't hesitate to build either caliber again. Used to have a 6.5x55, I liked that one too.
I think a 6.5 WSM would be an interesting proposition.
I think anything in 6.5 would serve well. Just figure out what weight bullets you want to fly, and get the barrel twist needed for them.
With the four choices on the poll, probably a .260....