Parents are clearly the people who should be better role models for children. Entertainment industry professionals have a lot of problems -- they're only human. Parents have a lot of problems too, but what they do and say does and should have more impact on children. They should be the role models.
Parents make better role models than anyone in the entertainment industry. Most people in that industry are a little crazy and care more about making money and having fun than what children watch and are exposed too. Parents generally are there for the kid and are able to set good examples.
Unless a child's parents are criminals, abusive, or deadbeat parents, they usually make great role models for their children. Entertainment idols are not good idols because they are often mired in drugs, get cosmetic surgery to look their best, and have almost unattainable careers. Children need a more realistic role model, and a parent makes the best kind.
Under a normal situation I would say that parents will make the better role model. They are there to push their kid in the right direction and teach them how to act and respond to different situations appropriately. Entertainment industry is more worried about their look and making money than anyhting else.
I do not believe anyone in the entertainment industry can be a decent role model compared to parents. Parents are in children's life on a daily basis, so if a child sees a parent doing drugs, then they will be far more likely to follow, just as they will be likely to work hard, if they see their parents doing the same.