I too own all three, and each have their strengths and weaknesses, which others have pointed out nicely.
If you want a true beater gun, the M44 Mosin is hard to beat, and the bayonet makes for a mean looking built in feature.
The mauser family will probably edge out the other two in accuracy, but the availability of non-corrosive ammo is short, and expensive; and you wouldnt want to have to clean immediately after shooting a beater gun.
The SKS is a good solid semi-auto, just dont try to turn it into an AK with accessories and such, and therefore compromise its reliability. Just a note, make sure to inspect your SKS trigger sear if you go that route and ensure it is not prone to "slam fire". Some of the newest imports have been having issues with this.
check out
http://www.surplusrifle.com and look at articles on each to help you decide.
Good luck with whatever you get.