It can be kind of overwhelming to make such a selection.
Me, outside of a couple of 5.56/.223 caliber rifles I own a .308 Win and I'm building a .300 Win Mag to suit me. I like the .300 Win Mag for a couple of reason, easy to acquire components for reloading and easy to find factory ammo.
If I plan to shoot past 200 yards on most game animals I opt for the .300 Win Mag. If I'll likely be shooting closer then the .308 gets the nod. If I could have only one it would be the .300 Win Mag hands down.
The .300 Win Mag is what I consider a 30-06 on steroids to be. The .308 is a 30-06 Lite. The advantage to the .300 is, for me, the amount of power it delivers at longer ranges. Making such a choice can be a daunting task and one that will have us second guessing ourselves until the end.
I look at logistics as part of my decision making process. If I'm in Podunk, AR and need ammo I want to know I can find it at the local shop without having to special order it. That alone rules out a lot of calibers in and of itself. I also want to know that I can easily find reloading components.
Me, I'd love a Mauser in .300 Win Mag but I like the .30 cals best. We can talk bullet selection and power charts all day long but the big factor is going to be you and what you want. I consider the 180 grain bullet to be the standard bullet for the .300 Win Mag and can move up or down from there depending upon the usage.
I'm sort of a traditionalist and have never warmed to metric calibers, 9.3 x 62 being the exception although I do prefer the .35 Whelen, and like traditional calibers which the WSM's are not yet. Maybe someday they will be.
I hope that something I said was of help to you. Good luck in your decision making process and Merry Christmas.
Biker