SKS: had one, I found the stock too small but it's fun to shoot, very simple and you can get a Tapco or else if you found the stock too small. Truck load of after market accessories. Tons and tons of cheap ammo.
Mosin 91/30: You can ALMOST disassemble the entire rifle with a flat head screw driver, very simple and robust design. The ammo is just a little more expensive than the SKS (still about 30 cents or less the round). Very easy to do a trigger job. Accurate but not Remington 700 accurate. Lot of after market accessories. A bit long but you get used to it. Some are just 100$!
Make yourself a favor and buy both