[Monkey Matt]

You are right to prefer a live-a-board if you are going for the diving. Islands boat dive twice a day and live-a-boards 3 times a day. It's not just the quantity though as the mobility of a live-a-board lets you cover more area and get both sides of the atolls. That said White Sands which is on the tip of S Ari atoll is the best spot for whale sharks and they do run day boats to the manta cleaning station on the other side of the Atoll. There is also a large wreck sunk by another resort nearby. The channel south of Dangethi, the biggest local island, has some great dive sites as well.
Stingray is a fairly good boat and the crew know their stuff so I am sure that they will get you to all the right spots.
I am not back out there until the 16th of December and I am pretty sure the other boats in our fleet are full. PM me if you want the company web site but you will need confirmed travel dates and I am unsure of the flight connections on our departure dates.