I bought a 6mm over a 243 because the 6mm with the proper twist rate and heavy bullets is a handloaders dream. It can be loaded to much higher velocities than the 243.
Having said that, I was once chasing a modern 250 savage bolt gun and couldnt find one anywhere. I finally settled on a bolt gun in 257 Roberts and never looked back. I now own 8 Roberts guns and deer hunt with them almost exclusively. Still a few new rifles chambered for it even.
The big advantage in the 6mm is that's its easier on brass than the 243. I have a custom barrel for my Blaser R8 that has a 7 ¼ twist. It allows me to seat the long, heavies on out without having to deal with the mag length of a normal short action, like the 243.
