Hey Beaner,
Although I don't do much scuba diving these days, I will say one of the best times I've had over here (for 300 bucks) was doing a 4-day liveaboard out to the Similian and Surin Islands. Albeit, this was some 5+ years ago, I doubt much has changed and this is one of the best, if not the best areas to dive in Thai waters. The only downer was the number of dive boats that go to this popular area from Khao Lak and Phuket, which can make the jostling for space and clanking of tanks frustrating when something of interest is spotted.
Our boat was spacious, the food was good and plentiful and the cabins/beds adequately comfortable - most operate on a double bunk, 2 sharing basis. Yes, the toilet was shared but always kept clean. Luckily, we were blessed with the other guests in our group being friendly and fun people, which only added to the experience. The instructors were 1st rate to boot. There were 4 dives per day available (you didn't have to dive them all, but we did), all at different islands/reefs, the last of which each day was a night dive in the early evenings.
If you're coming to Thailand to relax, spending some time on the beach and experiencing a little Thai culture and really cant do without all the fine trimmings, then stay at your resort and take a day trip or two by speedboat. I'm not sure how many dives you will get that way, as the islands are a ways offshore.
However, if you're a dive fanatic, then definately do a live-aboard and put up with a minor lack of creature comforts. You will cover many more dive sites, get more hours in the water and hopefully be left, as I was, with an unforgettable experience.
Surely, you will be here for at least 10 days, so why not do both?
Hope this helps.
Charlie :friday