Perhaps the single best website for comparing the different Medicare Advantage plans is that of the government itself.
Look at the CMS website
The Centers for Medicare and Medicaid Services (CMS) has a simple tool for comparing the premiums and out-of-pocket costs for all the plans by zip code. The site also gives the star rating system for each of the plans. When I tried it, in Southern California Kaiser Permanente’s HMO was the only plan with a rating of five out of five stars. Try it here.
Or hire a broker
Another alternative is to find a broker who clearly explains the advantages and disadvantages of both types of plans. Only when you have decided if you want Medicare Advantage or Medigap, then can you choose one of the many plans within each grouping. But note that all plans with the same letter (such as A, B or all the way through N) will have the same coverage. So all Plan As have identical coverage. Plan Bs differ from Plan As but all Plan Bs are the same in what they cover. So it goes with all the plans, regardless of which insurance company that underwrites the plan.
The coverage is set by regulation, either by the State insurance regulator or by CMS. It is a just a question of which insurance company covers your geographic area and at what premium — and which company you prefer to work with.