Jayph,
If you're looking for a logical way to decide, Perhaps I can help. But if it's emotion you're basing your choice on, then no one can make that decision but you.
If you are looking at factory ballistics, read the back of Speer #9. They chronographed actual factory loads and recorded the velocities. The .308 Norma just about comes out on top of every other .30 cal magnum. (even the .300 Wby) But that is because loads are chrongraphed in actual hunting rifles. The .308 Norma is factory loaded to 65,000 PSI. IIRC the .300 WBY is only about 58,000 and the longer freebore of Weatherby rifles causes some velocity loss.
That being said, if you throw handloading into the mix, then the .300 Win, .308 Norma, .300 H&H, and even the .300 WBY are all pretty much peas in a pod. Realistically, at reasonable hunting ranges, neither you nor the intended victim will notice the difference.
Bear in mind, that this then becomes pretty much an emotional issue. Some folks are impressed with the .300 H&H because a guy named Ben Comfort (IIRC) set a 1000 yd record with it back in the 1930's. Some folks don't like the double radius shoulder of the WBY propriety cartridges. Other folks think the .308 Norma is just plain magical. (Myself included). And yet, even others don't care for the short neck of the .300 Win.
But ultimately the choice is
EMOTIONAL! And if it's your gun, then it's your emotional. You have only to please yourself. What I think, matters not!
Grasshopper
