Assuming you are asking which health insurance is best for your parents, there are a few things you will want to take into account.
First, what type of coverage do they need? If they are retired and on Medicare, then they will need a supplemental policy to cover what Medicare does not. If they are still working, then they will need a policy that compliments their employer's coverage.
Next, what is their budget? Health insurance can be expensive, so they will need to find a policy that fits within their budget.
Lastly, what are their health needs? If they have any preexisting conditions, they will need to find a policy that covers those conditions.
There are a lot of different health insurance policies out there, so it is important to do your research to find the best one for your parents. This website has a lot of good information on health insurance: https://www.ehealthinsurance.com/ehealthinsurance/resources/health-insurance-basics