We used Magical Express once to the BWI, but it took well over two hours to get there. I know our experience wasn't typical, but my kids were so tired from waiting in lines to check in, then for the bus, and my son has asthma, so he was really tired. We took a cab back that trip.
We've used three different towncar services, and the one we love the most I'm sorry but I can't mention here. I think they still are a sponsor on Deb's website: allears.net. We've gotten very excellent service, clean cars, and we like the little grocery stop (usually Publix) on the way to the resort.
Really all our experiences with town car services have been fine, but the one I like the most I'm not allowed to post here. They all run about the same price, and it's so convenient to have someone meet you and just drive you away. We also don't usually check luggage, so it's much quicker than ME.