I say neither of the calibers listed, since this is your first rifle. I strongly encourage you to consider a 30'06, or 308 first. For a first time shooter, even those may startle you until you are used to how a rifle recoils. The 300winmag, though not a violent kicker, is very noticeable to even experienced shooters. My wife shoots one, however, she cut her teeth on an '06, and my 7mm mag first. The 338winmag, is a definite step up in recoil, and not for the inexperienced. Pain and severe flinching will develop, making shooting it accurately impossible. With practice and patience, one can work their way up to something that big, but its not a gun you just grab and go for the first time. I'm not bashing magnums by any means mind you, most of my rifles are magnums, but I was once in your shoes, and made the smart move in starting small and going up.