I've just started looking into this and it's not that easy to figure out. It depends on which state you live in, which meds you take, are they brand or generic.
Then there's the whole question of if you're doing regular medicare and adding part D, or do you want an advantage plan?
There are so many plans for each state it's a little overwhelming.
You can get a lot of info from the Medicare site:
http://www.medicare.gov/
if you just want part D, then click on the link and enter your zip code on the following page. Then you fill in all your meds and have it do a search ....
I'm thinking of maybe using the Allsup Medicare advisor:
http://www.allsup.com/medicare-advisor.aspx
I may give them a call and then try to decide if they can really help me sort it all out.
At any rate, there is no one Part D plan that is best for everyone.