I have used Super Shuttle twice. The first time it went smooth as silk and I loved using their app to track my van. The second time, well, the van nearly broke down and couldn't crest about 40 mph for the last part of the trip. Plus this van was kinda dirty too. The pickup van was super nice, but they mixed up my flight number resulting in a very early pickup. I just went with it, but I never gave the time, just a flight number, and I think their system thought it left much earlier than my flight did, so I was at the airport like 4 hours early at like 4 in the morning!
Any of the services have a chance of fouling up somehow. I think the key is to give yourself plenty of time. Good luck!