AK's although quite reliable are not known for their accuracy. It would be a poor choice for a varmint rifle.
Mini's of old were not as accurate as the newer ones. So if accuracy is a determining factor to use it for varmints, a new Mini-14 Target would be better than an older used Ranch. Although I do have confirmed prairie dog kills at 450 yards with an older mini Ranch.
What would be cool is if they would chamber one in 5.45x39 so you could have cheap ammo.