That's entirely dependent on your shooting style and the weight you want to carry. My favorite is the 300 Win Mag Sendero but it's best when shot from bags or a bipod. the SPR is lighter and less expensive but still heavier than a sporter. If you shoot mostly unsupported then a sporter (ADL/BDL/CDL) would be a good choice. Maybe a titanium action mountain rifle if you want to carry it in rough terrain, have the money, and can find one. I'd recommend not less than a 24" barrel for a 300 Win Mag. The Sendero is 26".
I like the Rem 700 for "medium magnums because they have 3.6" magazines which allows handling longer low drag bullets. The SAAMI OAL of the 300 Win mag cartridge is only 3.34".
That allows a considerable performance improvement with handloads. Something you don't get with a 300 WSM
in a short action.