Duh! The 6.5 Sherman hands down
Well, I guess I may have a little bias! Seriously, I designed the Sherman because I am a big 6.5 fan and shot a lot of elk with my A.I. before I designed the Sherman. There are a lot of things to like about it. Brass is abundant in many different brands. Case forming is quite easy. 3200' with 140's in a 26" barrel. Great accuracy and case life between 3100-3150". Because of the minimal body taper and 40 degree shoulder, case stretching is minimal. I have 1500 rounds through my 3 groove, 8 twist Lilja and it it still shoots .3-.4". Ya, it has lost a little accuracy. Highest velocity with a .470" case head possible and still has a good neck.(.300") It is my belief that the longer neck and 40 degree shoulder keep the flame point more confined in the case rather than directly into the throat which causes faster erosion. (picture the flame on a blow torch) hottest at the tip!
Two more guys have committed to building one as of last night. It will be fun to start comparing notes! I now have it available with a .294" neck and also a .297" (no turn) version. I also have a "max" version that has a .025" longer body and adds approx. 1 grain of capacity. My rifle will shoot almost ANY powder from 4350 up to Retumbo with less than .5 moa accuracy with 140 bergers or A-max. Let me know when you want one