Provider reviews of health insurance?

It would be best (as someone else said) for your family member to ask their provider, since they're the ones that typically deal with that condition.  Otherwise, generic reviews from providers are just going to tell you which insurance companies reimburse them the least.  I would always hear, "Oh, my brother-in-law told me not to go with XYZ Insurance, because they're not good."  "Is your brother-in-law a doctor?" "Yes, how did you know that?"  "Because your brother-in-law gets paid the least from that carriers, so he's bitter about it.  Otherwise, they're a good company."

you could ask his docs or their office managers, or google the company names of the insurances he's considering.

Given that you have a family member with a particular condition and these authorization issues, don't you think that talking to his specific doctors about their views of the insurance options would be best? And don't you think you're more likely to get information on whether there's some sort of reliable website you can look at from medical professionals themselves -- such as your relatives' physicians?

I have to warn you that most often doctors don't deal directly with the insurance companies anyway and aren't the best people to consult. They have staff who handle these things. They'll get involved if they really feel the need to argue an insurer's decision, but usually it's staff interacting with the insurers. 

Insurance has a contract with the doctors.
If the doctor has a contract with the doctor, you can surmise that the issues they have with the insurance company do not outweigh the access to in-network patients or the associated income.

If there are specific issues that you don't want to deal with, with insurance look for insurance policies that don't have that issue.
- all insurance will require some "prior authorization"
- HMOs and medicare advantage plans would require this more since it's part of the business model.  Look for PPO plans or if on medicare a Medicare Plan F, G, etc