We too had problems with Happy Limo. We were waiting and waiting at the port and couldn't even get anyone on the phone! I realize that this was a one time experience and couldn't have happened with any towncar service (at least the being late part, I don't know about the fact that we couldn't reach them by phone). However, my biggest complaint and the reason I won't give them another chance is that I contacted them about our problem after we got home and I never got an acknowledgement or response from them. At the very least, they should have responded to apologize. So the bottom line is that any company can have an isolated incident, but I think a good company tries to maintain good customer relations.
We too used Cartier towncar on our recent trip. They were fabulous -- professional, curteious, and on time. And I too like the fact that I control the gratuity instead of being obligated to 20% if service is poor.