I'm assuming the question is the rich Uncle left me the choice of one of the two rifles, and that it will be the only rifle I will ever again use.

Well sacrilege that it may be, I would choose the bolt action if it is a nice light Mauser 98 actioned rifle. Light so it can be carried a lot.Accurate and handles well, and suitably scoped for a variety of situations.

Doubles though nice they are don't make good long range plains game and mountain rifles, which a .375 with a good accurate light bullet would do. Nor do they have more than two rounds ready at hand.

Now that bolt paired with a good .450 double would be perfect