If you don't care about a party scene, you should check out Turneffe Island Lodge. It is much closer to the best dive sites. The best dive I did while I was there were right out front.
I spent a week at Turneffe Island Lodge in April 2005. I went on my own and had a great week. The island wasn't completely full -- about half of the guests were divers, a quarter fisherman, the remaining quarter snorkellers and/or partners of the fishing and diving types.
It's a nice compromise between a land-based holiday and a liveaboard. I had not done a liveaboard when I did this trip.
All of the dive sites are a 5-10 minute boat ride from the island. These are some of the best dive sites in Belize. Our 1st dive of the day was always the Elbow which is a well known site in Belize. I saw my first hammerhead there on the last day.
You set up your kit at the dive center the first day and then the guides change over tanks and have your stuff on the boat for every dive. You can do three dives a day (verusus 4-5 on some liveaboards) two before lunch and an afternoon dive. One day the afternoon dive is replaced with a night dive. One day per week the whole island goes to the Blue Hole and Lighthouse Reef. They have the time on the island set an hour ahead of the mainland so they arrive before any of the day boats. We were the first in the water and many of the other boars were just getting in as we were doing our safety stop. Aside from the Blue Hole day, most dives were fantastic and relaxing drift dives.
At the time I was there the dive guides were local Belizean guys and were excellent. The managers tend to be international types -- they tend to do the courses and the first check-out dives. All of the above were great -- competent divers and friendly on land.
The basic rooms are nice and comfortable, but I would recommend that couples splurge for one of the cabanas. The staff leave tea or coffee for you on your balcony/patio early in the morning -- not a wake-up call per se, but a very civilized way to start the day.
Lots of hammocks and shade for reading books or chilling out. A swimming pool as well. Just watch out for the falling coconuts.
The 'kitchen ladies' outdid themselves at every meal. All breads are made from scratch. The only complaint I had on food was that some of the lunches were pretty heavy (think seafood alfreddo) considering we were diving not long afterwards. I just asked them to leave sauces on the side. Another guest had pretty severe diet restrictions and the staff seemed to accomodate them with no problems. There are fresh baked cookies each day. Drinks (including sodas) are extra but everything else was included.
If I go back to Belize it would be hard for me to choose a liveaboard or other land based option due to the quality of the dive sites we visited each day. I'd go back in a minute.