I have used Greyline. Good service, very convenient. They pick you up at your hotel, go to their "departure centre" where you board a bus designated for the attraction you booked for. On the way back they take you straight to your hotel.
The driver we had for the Seaworld day was great, they share lots of information on the ride down, facts and tidbits. Our driver even veared off and drove us by the old monastery.
You will enjoy the experience!