Don't automatically buy the AARP Prescription Plan. My folks did, because they automatically believe that AARP just HAS to be the best in everything. Consequently, they ended up paying full price all the way through the donut hole.
Unless you have good durg coverage from your previous employer, you should consider choosing one of the Medicare plans, because if you don't you will be penalized for each month that you haven't joined, if you ultimately join.
Go go www.medicare.gov
and click on the link right in the middle of the page "Compare Medicare Prescription Drug Plans". That will take you to a website that will compare all the plans available to you based on the list of drugs that you enter. The plans vary WIDELY. Some charge you a deductible, some cover the donut hole some don't. This site will give the the estimated TOTAL annual cost to you for your drug costs.