22-243 because I have three of them. The 22-6mm does about the same but the 243 cases are found everywhere. The 22-243 A.I. holds more powder but I don't think you need it for 3500 fps and long barrel life.
I use Rel. # 19 and Rel #22 with CCI primers, 243 brass sized down to 22 and then neck turn for a .256 neck, run 75 grain A-Max bullets out to 3790 fps.
This round will shoot through a bowling ball at 1000 yds with 47.4 grs Re. #19 and 75 gr. A-Max, has shot a 1.75" group best at 830 yds, and kill at 1151 yds. 100yd groups are 3/8" down to one hole 3 shot groups with some 1/4" 10 shot groups, depends on blood pressure that day.
I shoot a Savage 112 long action for more room to load, a douglas XX barrel fitted by Sharp Shooter Supply's owner Fred Moreo, he has been building my barrel set up since 1997. I shoot a 1-9 twist and have shot 35 V-Max bullets up to 5600+ fps for fun and killed Prairie Dogs with that little bullet out to 600 yds.
I am building another 22-243 right now with Savage Target action, F Class stock and a heavy straight contour barrel in 1-14 for 4500 to 5000 fps shots.gun)gun)gun)gun)gun)gun)