I'm not 65 for a few years yet, but I dug into the whole Medicare options out of curiosity. It is very confusing with the Advantage Plans, I don't believe there are any I would personally consider when it's my time. Regular Medicare covers 80% of in-patient and out-patient services, at any facility or doctor that accepts Medicare anywhere in the US. There is no max on that other 20%. That's why Medi-Gap, or Supplement policies come in to play. They are policies by major insurance companies BUT, they are completely locked in to whatever Medicare covers, they have no option but to pay. their part. If its covered under Medicare, Medicare will pay the 80% and the Gap Policy will pay the 20%, there are no ifs' ands', or buts. The Gap plan G is the top tier currently and is a bit expensive as a monthly premium but the only additional fee is like the 1st $226 a year as a Part B deductible. Gap Plan N is a little cheaper monthly and includes some co-pays for office visits, etc, and doesn't include "excess charges" of up to 15% over standard Medicare rates, supposedly that's rare (~ 3% of doctors/facilities charge those). The one that interests me though, when its my time, is the Supplement Plan G-HD (high deductable) which is currently $2700/year. But that's after the primary Medicare pays its 80% first. So unless you're really injured/ill, you likely won't hit that in a given year. Many insurance carriers offer the Gap plans and they are identical across all, its by law that way, so a Plan G is a Plan G is a Plan G, etc.
Now, Advantage Plans are where the CMS (Medicare Fund) pays the insurance carrier like $1,000/month for each participant to "take over their healthcare", so in these cases, the insurance companies are deciding what services they will pay, which network of doctors you can see, etc. Its the same thing where you may need pre-approval to see a specialist, get a test, etc. They decide. They also throw in dental and vision but its limited, and a gym membership. And it may be "free" to you on a per month basis (You still have. to pay the Medicare Part B monthly premium). But the plans can and do change every year, you really have to keep track of them every year. People are attracted to them because of marketing and it sounds good when they are free/cheap. But the healthiest we'll probably be is when we first sign up, and Advantage Plans are great - until you need care. And there is a limited window after initial Medicare sign up where you can try either standard Medicare (and Supplements) or Advantage. After that, you may still switch, but you will be subject to Medical underwriting. They expect that if you want to switch back to Medicare, you may have a major issue. With standard Medicare, you are guaranteed entry when you are first eligible regardless of preconditions, after that window, maybe not.
Yes, standard Medicare + Gap isn't cheap, but when you need it, its pretty straightforward. In my state last year, the retired state workers were being pushed into an Advantage Plan as their only option (previously they had a choice between Advantage and standard Medicare) and protests ensued, I think the same thing happened in NYC.
There may be good Advantage Plans, but, they can change year-to year. Just be aware.