i'm a nurse and i'm just prejudiced against HMO's.
i personally don't like to be limited in care i seek. like picking a dr or hospital.
and sometimes the care is doled out. IMHO.

however, if you have to watch $$$ an HMO is a good deal.
i'd look around for a high rated one. for instance here in CO Kaiser is rated very high.

if you're in original medicare you can go anywhere you want; dr or hospital.
and, if you are one to travel you have access anywhere.

however, there's always a but, expect the costs to be higher.
i believe that i pay a lot for my meds. bear in mind that i'm on a lot of meds.
i pay for my medicare premium (about $100), then my part D premium ($150) plus the co-pays for my meds. then when you fall in the donut hole you may be required to pay up to about $4000 before your costs go down.

plus, i have a hx of needing a lot of care. so i get an AARP supplement policy. and i ended up having breast cancer and needing surgery. so it turned out to be a Godsend that i had the extra coverage (another $150) and all these costs are per month.

go to the medicare.gov site and you can compare plans for your area.
you can also call their representatives and they're very knowledgeable.

another thing i did when i was first deciding on all this last yr was talk to my pharmacist (Walgreens). they were able to run out info on about 6 plans in my area based on the meds i was on. VERY helpful.