You get what you pay for, and with Supershuttle that is a slow shared van. On the way to the airport I was fine; they arrived with plenty of time for my flight. But on the way home, the van had partially filled up and already visited all three terminals at PHX, and was almost off-site, when the dispatcher called, so we looped back through all three terminals to fill up the van completely. I get that it's their business to run full, but I felt like Michael Corleone. "Just when I thought I was out... They pulled me back in!"
If you have patience, then SS fits the bill, but with deals for off-site parking I find it no more expensive to leave my car off-site than pay round-trip shuttle service.