If you are really into diving and want a good sampling of sites, why not try a LOB that goes through east coast peninsular Malaysia. Go check with Penetration Divers in Tanglin Singapore and see what the schedules are. You can just call them up.
If you can afford the extra time and flight, I would recommend Mabul, Kapalai, Sipadan, Mataking... off Sabah. Once in Sabah, there are other things to do besides diving.
If you can afford the extra time and flight, I would recommend Mabul, Kapalai, Sipadan, Mataking... off Sabah. Once in Sabah, there are other things to do besides diving.