.243 for practical, .257 for cool (and elk if that's a possibility).
I often cruise around on the web looking at the availability of stuff to feed rifles I'm interested in, and the .243 wins the brass and ammo contest, hands down. Not that the .257 can't be fed, just that it may take a little more effort. Not long after I picked up my old Sako, I scored 400 Sierra 100gr PH blems for a ridiculous price. Brass at that time was scarce for almost everything but .223 and .308, but I found Hornady .243 brass on Amazon and Grafs (same lot number, go figure). Also consider that if things get tight again, a .308-based round can be fed with the mountains of surplus brass out there.
Now go buy something and report back so we can all dump on you for buying the wrong one.
