Between those three options you’ll have to decide what your plan is to do with the rifle. To hunt open country out west for deer and elk the 6.5 PRC. If you plan to bang steel I’d go with 6CM. If you plan on steel and keep shots at big (elk, deer) game under 500yds I’d go with 6.5CM.... all three cartridges can kill animals and bang steel, some are better suited at than others at each.... that’s just my opinion. I’m sure people will have different opinions. Lots of ways to get it done haha