Being the Fossil that I am, I'd have to vote 6.5x55, and if you just have to have a modern cartridge, I'd go 260 Rem
Potato, Potatto. It will be interesting to see in a decade or so who makes the cut, I just don't see them all surviving. Add to the above, the 6.5x47 also a very interesting little round. I was sniffing around for a TRG in a 260, looks like they are all sold now, but Sako is making them in Creedmoor, so who the hell knows. Maybe the Creedmoor will put the others to bed, I doubt it, but it's fun trying to guess.