We've done towncar transportation in the past with Orlando Airport Towncar Service, and Orlando Luxury Transportation. Both went smoothly. We had also booked Happy Limo for an upcoming trip, but had to cancel when the plans changed, and although I can't review their transportation, I can say I was favorably impressed by their customer service and communication.
There are tons of similar services out there with fairly similar price points to one another. I typically check recent Yelp, Google and Tripadvisor reviews, and go with whichever of the best-rated and longest-running services (not a fly-by-night!) is most reasonably priced for my dates and vehicle.
Do make sure you read the fine print, though! Some companies include the driver's gratuity in the price, and some don't. Some will add a "service charge" or fees for late/early pickups, and some don't. Some include taxes in the price they quote you, and others add it later. Almost all will include a free grocery stop, but make sure you know how, and how early, to make that request. Also, some companies will charge a cancellation fee if you have to cancel your trip (changes are free, and of course they'll try to accommodate you if your flight gets delayed, etc.), while others offer free cancellation, so you'll want to take note of that, too.
