I have used Aerocity for the past 6 or 7 years and have been very pleased. I made reservations online for transport from Barajas to hotel and back again for a return date(which I confirm at the airport before heading to my hotel after my arrival in Madrid).

It is important for people to know that your driver may stop to drop off and/or to pick up other passengers en route. It is sometimes nerve wracking when we are waiting for someone to be picked up en our return to airport and the customer is not there or is not yet ready. However, I found that the driver does not wait long before heading out (many times without the "pick up"--for which he has called his supervisor to report that he was unable to locate customer, etc.). The driver seems well aware of their time constraints. So, be ready for your pick up!

I have reserved through their web site and requested a quote for transport. A response to my email followed within the business day.