I would say the Hi Point carbine for the following reasons:
1. Shorter and easier to maneuver in/out of the vehicle.
2. Easier to replace if stolen. (SKS's are no longer made)
3. 9mm is enough to penetrate a door or most vehicular glass.
4. You won't have to worry SO MUCH about over-penetration.
God forbid you shoot your intended target and then strike innocents behind it. I don't think you would want that on your hands. Also, if your aggressor is out of range for a 9mm carbine, you have enough time to get in your truck and escape the danger. Just my
.