I've never really had many issues with Discount cab. I usually use them when I am going to and from the airport. The drivers are usually very courteous and friendly and prompt at arriving. There's nothing worse than an awkward conversation in a cab and I've never encountered that with Discount. I have with plenty of other cab companies and am now pretty picky about who takes me to the airport.
I do think they need better people answering the phones to take reservations though. There have been one or two times I've called and schedule a pickup the night before a morning flight only to call in the morning to check status and find out it was never entered into their system. I shouldn't have to play babysitter.