I have worked on both sides of the Medco issue. In the past I found it to be the most infuriating drug coverage. They really made their patients jump thru hoops, and at times had insane rules. They were difficult to deal with on the phone, ultra time consuming, at the pharmacy level, and infuriating in general.

But we have also had it as our family plan. No choice. We have Federal Blue Cross thru my husband's job. Medco was dropped 3 yrs ago, but it is back this year. I have to say, they are a bit better than before. But they still give me the heebeejeebees.
They can also be very slow to send your drugs thru the mail.
In the stores we have Caremark, and only Medco for the mail away. (don't ask me why).

One nice thing they did was give us 4 free copays for the mail away per year on generics. This helps with one of my prescriptions. Medco is BIG BIG on generics. So be prepared for that. But one example of infuriating stuff: I had just sent my blood pressure RX to them, and they did not send it. Instead they called me when I was not at home, so I had to return the call and wait on the phone....then to only find out the delay?
What was my email address?? (the forms don't ask for it). Well, it is the same as before! And the person who helped me said it was clearly on my file! STUPID! Things like this are small...when they hold up your order for 2 weeks or more for some other stupid reason, they become infuriating!