Double Star is excellent in quality, better than most out there and a cheap price to boot. Some claim they are on par with larue tactical. I don't know, I'm happy with my upper and lower.
Can't help much on the AK, I have an old norinco that does well. Never grouped it, but hits what I aim at. Most folks claim they will go 2" or so. A lot of guys are buying saiga and putting standard AK stocks on them, claiming they are more accurate than the assembled parts kits the gun shops are selling now.