I booked Happy Limo for my parents last trip. (we arrived a day earlier and picked up the rental car)
I was very pleased with Happy Limo. Leonard was on time or early, very courteous, clean car, etc. I would not hesitate to recommend them and would use them again. (although we personally always rent a car)
It seems that no matter which service you choose, someone sometime has had a bad experience with every one of them. My advice is to make sure to confirm confirm confirm--and then do not hesitate to call if they are even ten minutes late--it didn't happen to us with Happy Limo, but have heard of small mix ups with all of the companies at one time or another. I think unfortunately it depends on the individual drivers--we're all human after all. Be prepared with an alternative plan if need be.
All that being said, Happy Limo was awesome.