The common mauser and mosin are both 3-4 MOA rifles. However if you look at particular mauser variations such as the Swedish M96 and the Czech M98/22 or at the mosin variations such as the Finnish M39 or the M91/59 you will find that these rifles are 1-2 MOA. I have dozens of both rifles and enjoy the accurate ones best as I target shoot and hunt with these rifles. What separates the rifles for me is the much more available and generally cheaper 7.62x54 ammo. Both rounds are pretty close in power and ballistics and both were designed well over one hundred years ago. Except for the variations I mentioned above, prices for the mosin are generally much lower than the mausers.
Because of the Finnish mosins, I would have to vote for the mosin.