Assuming we're talking about a Kar98k pattern rifle (I would include the Czech VZ-24 and Yugo M48 in this category), I'd say it's six in one hand and half a dozen in the other. Both rifles have proven themselves to be boringly reliable, both are more accurate than most shooters are capable of appreciating, and the difference in terminal performance between 7.62x54R and 7.92x57 is negligable. I find the Mauser to have a more easily manipulated safety and it is smoother to load with stripper clips. The Mosin-Nagant, on the other hand, seems to me to have a smoother bolt throw and iron sights which I can see better. While the Mosin is much longer, it doesn't seem to be as muzzle-heavy as I would expect and thus both rifles balance about equally well in the hand.
Smith, and Wesson, and Me. -H. Callahan
Well waddaya know, one buwwet weft! -E. Fudd
All bad precedents begin as justifiable measures. -J. Caesar