If you get the Saiga, would you leave it in an unconverted configuration, or would you convert it to pistol grip and give it the ability to take AK mags?
If you plan to shoot mainly from the bench, you may consider the SKS (assuming that it is in factory condition). The fixed 10 round mag is much more conducive for shooting from a benchrest, or from a prone position. The Saiga with a factory mag may be similar, but if you convert it to take the 30 round mags, will be much higher off of the bench/ground than the SKS with 10 rounds. There are smaller AK mags available, such as 20 rounders that help with the AK.
Shooting from a standing position, not that much difference. The sight radius on an SKS is a few inches longer, which leads some to believe that it might be a little more accurate overall.
I have had a Chinese SKS, a Yugo SKS, and a converted Saiga. I enjoyed the Chinese SKS and the Saiga, didn't enjoy the Yugo SKS as much. The heavier receiver, along with the grenade launcher and other "stuff" made the Yugo just a little too heavy for me. I would still love to find a good Russian SKS though.
Good luck, whatever you choose!