There is a big difference but Medicare is not an option unless you are 65 and a legal resident of the US. There are not many options for people over 65 other than straight Medicare or Medicare approved private insurance such as the Medicare Advantage plans like I have. The Medicare web site lists the private plans available in your locality. Most people who have straight Medicare also buy a Medigap policy that covers the deductibles, etc. that Medicare doesn't. The premiums are pretty cheap. My mother switched to a Medicare Advantage plan a year after having regular Medicare. She had the option to continue paying the government for Part A and B or to pay the insurance company directly which was cheaper. I handled all her financial affairs so am very familiar with it.

All private Medicare Advantage plans have to be approved by Medicare and meet their standards. They have to accept everybody that qualifies for Medicare and lives in a locality where the plan is offered. The insurance companies offering Medicare Advantage plans are paid a monthly fee ( $1000+ /month ) from the US government for each subscriber. The private companies compete with each other on service and cost. Some are very good and some are not so good. This can easily be checked out by looking at their ratings. Many of them do not charge any premiums and offer much more extensive coverage than regular Medicare. These private plans are not available in all parts of the country. They are very strong in California. There are currently 10 million subscribers to the the Medicare Advantage plans.