I have an SKS. Fun rifle. Ammo can be pricey, gun always shoots well even dirty. Sighting is a little pita but once you get used to it its not bad.
For ar a nice affordable base model DPMS or Rock River Arms would be a good starting point if your going to mod it up. You can buy a lower from a local gun shop and buy pieces online. They are easy to assemble. I built my .308 AR10 from scratch (all collected pieces) also assemble most of cosseys AR10 as well.