SuperShuttle hasn't served Denver International for a while. I remember seeing their vans frequently, but I have to imagine here the new airport train as well as ride sharing ate their lunch. I haven't not used the train ever since it opened.
I use Green Ride Boulder which is the same concept as SuperShuttle but way better execution. Scheduled rides, most people get on and off at the office, but they will drop you off at your door after the office customers.
i saw so many of their buses and vans engaging in wildly dangerous behavior when the weather was bad, along E470 and further north. i assume their insurance cut them off at some point.