I'm certainly no expert but, from 5 years of personal experience:
The plans that are available to you are dependent upon where you live*. Also, the same plan in one city might be much more expensive than the same plan in another city. And not all plans are the same everywhere or even available everywhere. The only sure way to make a correct decision is to gather all the facts (and go to the free seminars if you can) and lay out all the available plans side by side. Then, score depending upon what is most important in your personal situation:
Monthly premium? Out-of-pocket? Deductibles? <-very important!
Can you use current doctors? Do you require pre-approval to see specialists?
What is (or is not) covered? Any exisiting conditions to consider?
..And, if possible, try to get info on how responsive the company is (from friends, if possible)
In a similar vein, how do they handle prescriptions? Will your current medicines be covered equally by all plans? Will the prescriptions cost the same in each plan?
Some plans (Humana Plus used to) provide free membership to YMCA, Well-being courses, etc. Ask about it.
Everything changes each year (or has for us). Just sticking with the "same" company from year-to-year might be the easiest (but often, the most expensive ) solution.
Growing old is not for wimps....
*Plans are dependent upon the demographics of your area: Average age, lifestyles, education, medical facilities and professional care available, etc. are some of the factors considered. Example.. Folks in Appalachia have less access to health care and folks in Florida are (on average) much older --so their costs are higher.