We used Happy Limo once. The driver was at the wrong place at the airport. It took us about 30 minutes to locate him. He then did not know how to get to the port. He asked us for directions! Thankfully, this was our second
Disney cruise so we generally knew the way. On the return trip, the limo was about 45 minutes late. When we called Happy Limo, we got only the automated message. When the driver finally showed up, he fessed up that he was late because a police officer ticketed him for speeding (yikes!). He also did not have any of the car seats that we had confirmed. In the end, Happy Limo incorrectly charged us twice for the trip, but when I called them, they took care of it.
Other than that, our experience with Happy Limo was fine

I will say, however, that the cars were very clean and the drivers were very nice. I guess the company had two bad days because most of the reports on this board are very positive about them. Therefore, I guess I would cautiously recommend them.
For our upcoming trip, however, we are trying a different company. I contacted Tiffany based on the feedback from this board. Unfortunately, I kept getting different information from different agents each time I called, primarily in regard to car and booster seats. I was also told by one agent that the internet coupon did not apply for the MCO to Port trip, even though it seems like it should. Therefore, I have booked a reservation with
FL Tours. They are a bit more expensive, but they seem like they have their act together. Their web site reservation form at least has an option to add car/booster seats so, hopefully, the driver will arrive with them.
The bottom line, however, is to mentally prepare yourself for everything when you're traveling and to not let anything ruin your trip. Have a great time!