How much time are you planning for your trip and how much diving do you like to do? What other things do you like to do on vacation? Last year we spent a week on Grand Cayman followed by a week on Little Cayman.
Keep in mind that the "wait to fly after diving" rule does apply to the short flights to and from GC and LC so you have to figure that into your travel plans. What time of year do you plan to travel? Planes can only land and take off from the LC airport during daylight hours, so during winter that shortens the window for available flights.
We love the Little Cayman Beach Resort, it is a small, reasonably-priced, diver-dedicated, all inclusive with an onsite dive op, but the Southern Cross Club is more upscale, and more expensive and it is also a popular venue.