I hear a lot of people talk about AARP as if it were an insurance company. It is not. In reality all that is happening when you see AARP as part of a name of a health or drug insurance plan is the private insurance company paid AARP a fee to use the logo. For many, the AARP "stamp of approval" means a lot. I don't have a clue how AARP vets those offerings nor what kind of fees they charge to use the logo. That is why the names of all the AARP plans are complex. For each offering the name has to be unique to the insurer and each insurer has several offerings.
I do know that the underlying insurer - whether United Healthcare, BlueCross/BlueShield and so on - does have a rating so the best thing to do when deciding what plan you want to buy is to evaluate the reputation of the insurer. There are a few ways to do that. In the "Medicare and You 2011" book at the back of the book there are ratings associated with the plans they profile. Your state SHIP (State Health Insurance Assistance Program) also has user ratings associated with plans offered in your state. You can find the phone number on medicare.gov. Also, ask your friends and your doctors what insurer they prefer. Sometimes an insurer is slow to pay or onerous about processing claims. The doctor's accounting office usually has strong opinions about who they prefer.
Comparison pricing is essential whether you are picking a medicare advantage, drug or a medigap plan. I strongly urge you to look at medicare.gov planfinder to do the comparison. It is the best example I have ever seen of your tax dollars at work to give you great information.