I agree with Arturo. I just returned from Spain, and I had reserved with AeroCity. It really did no good. When I showed up at their counter, they were confused and unaware of my reservation. They still needed to call around to find a van that was available to take us to our hotel. It took half an hour, and there were several other passengers waiting as well. We had given AeroCity a half hour to find a van and then we were going to take a taxi, so they can in just under the wire.
AeroCity is cheaper than a taxi, but be prepared to wait whether you have a reservation or not. It just depends on how many people need their services at the same time you do.