I don't know anything about Moreton, but my first major scuba trip was to Byron (report
HERE). It still ranks as one of the best places I've dived, and now I've been to Cozumel and Indonesia and the British Virgin Islands and Hawaii. We dove with Sundive, and liked them a lot, although I know that today, the time limitation on the dives would annoy me a little.
The life there is amazing. HUGE schools of fish, big and little; rays, sharks, turtles and many kinds of nudibranchs, as well as healthy, colorful corals and sponges. It wasn't difficult diving at all, although sometimes a little bit surgey, and it wasn't terribly deep. It was just, plain fun.
If you go there, I'd also recommend the place we stayed, Planula Lodge. It's a little ways out of town, but very quiet, and completely diver-oriented. The owners are both avid divers, and they have a lovely library of reference books upstairs where you can try to identify what all the things you saw during the day were.
Byron Bay also has some excellent restaurants and shops.
I'd love to go back.