My wife applies for Medicare in March. So I've spent about 15 hours on line the past couple of weeks researching the heck out of the best way to go. I knew next to nothing about Medicare/Soc Sec a month ago. It's not such an easy choice between Orig Medicare + Drug plan, or a Medigap plan (F,N,G) + Drug plan, or a Medicare Advantage Plan (HMO, PPO, etc.) for which nearly all include a drug plan. Statistics say about 1/3 are enrolled in MA plans and 2/3 in Medigap plans. Plan ratings don't matter much for Medigap as those benefits are standardized among each lettered plan. HMO/PPO ratings could be an issue. All of them in my state have ratings of 3.5-4 stars out of 5. You will always find complaints. A couple of insurers in my state stick out for "bad" reps, yet they still get 3.5 stars. For me, plan coverage details are what's most important.
If you're quite healthy and can expect to stay that way, the HMO/PPO plans seems the most reasonable. But I found that the "cheaper" HMO plans (some with $0 monthly premium and $0 drug plan deductible) bury the medicare part A $1316 deductible in your first 3-6 days of a hospital stay...and most only offer 20% co-insurance on the outpatient hospital visits (others might cap those costs at $200-$750 per visit but make up for it with a higher monthly premium). The Medigap plans offer A-N selections (not in all states) but it seems to me that only the F, N, G plans make sense out of the 10 types offered. While they all cover the $1316 part A deductible, that gets paid for in the monthly premium. Medigap plan premiums will range from $145-$295/month premiums for "competitive" plans in my state....they can go higher for non-competitive plans. Most states won't allow you to switch from a MA plan to a Medigap plan after you've had your plan for a year... w/o first having to go through pre-screening/medical evaluation. That's not the case for your initial 7 month medicare sign up period (guaranteed issuance). Connecticut and New York are guaranteed issuance states that give you more flexibility in switching plans. 3 other states do things a bit differently (MA, MN, WI?).
No matter what plans you sign up for, you still pay the $109-$134/month medicare part B premium. Some will have to pay a part A premium if they don't qualify on there own (or spouse's) work history. Only the Medigap plan F covers all the part A and B gaps in Original Medicare coverage. It's also the case that you will pay the highest premiums for a Medigap Plan F. Plans F is being retired for new enrollees in 2020 because they gov't wants everyone to have more "skin" in the game with premiums (previous enrollees will be able to stay on). No one seems to know if Plan F premiums will get out of whack past 2020 as the member pool shrinks. With the pat D prescription plans or drug coverage, there are always gaps, if not just the large "donut" hole which can run you thousands before you reach the catastrophic care coverage rate of "only" 5% co-insurance when you're out of pocket expenses have exceeded approx $5K-$10K depending on plan.
In the case of very rare extended medical care that exceeds a year over what Medicare authorizes (1 yr + 90 days + 60 reserve days), or Skilled Nursing Facility Care that exceeds 100 days or more, you typically pay all costs. The only plans I see in my state that say differently are the United Health Care HMO plans (ie say they cover in-patient stays "beyond 90 days."). None of the Medigap plans A-N say that. Then again, most will never have to deal with a hospital say longer than say 1-2 weeks. The first agent I talked to said that with a a plan F you never pay anything more than their monthly premium...EVER. He was emphatic on this point. But, go beyond the limitations of original medicare for hospital or SNF stays and you can pay more...a lot more. At least that's my understanding so far.
I'm still tossing things around for a Medigap Plan F/G/N, and a number of HMO plans in my state. The choice is not that simple imo. You have to know what your health situation will be in the next several years to pick the most advantageous one. Literature I read seemed to suggest that those starting off on Medicare Adv plans often made the switch to Medigap plans down the road as they got fairly sick. Then you have to deal with pre-screenings, pre-existing conditions, coverage being denied, etc. Fwiw, in my state AARP teams with United Health Care of their only "endorsed" PPO plan.