7 mm mag or 300

You are leaving a LOT of variables open and unknown.
The 7mm Rem Mag, 7mm STW, 28 Nosler, 7mm Wby Mag and the 300H&H, 300 WSM, 300win mag, 300 wby mag, 300 ultra mag, 30 Nosler, 30-378 wby are all capable of extremely fine accuracy.
At 250-300 yards a 300 Savage will do on deer/pronghorn.
Are you hunting deer or elk/moose?

If you had two rifles capable of producing accurate groups one in .284 dia and one in .308 dia. It is literally a toss up.
For a deer rifle I would favor the 7mm rem mag over the .300 win mag. If you plan to double this rifle for an Elk hunt in the future, maybe the .300 win mag.

Either way the 7mm rem mag would make short work of an elk hunt too. I just feel like the .300 win mag is more than necessary for a deer only rifle.