Disclaimer: I've only used union cab when I've made a telephone booking 24 hours in advance.
I've been in a union cab for about 4 round trips in the last year. Every time I've called ahead and scheduled, the respective cab drivers have either been there 5 minutes early or on time. I've never had a rude driver, and each driver was really helpful with heavy luggage at the airport. They are not as cheap as the share-ride cabs (like badger), but I felt a lot safer and more comfortable in a union cab.