Highly recommend you receive course certification in East Malaysia.
Our family members enjoyed their certification sessions under Nitrox and PADI certified agency. The dive professionals continuously invent spots and we are pleasantly surprised at results from their customized surveyed locations all over the islands. It is one of the few agencies to conduct intensive classroom and open water courses to match students’ schedules.
Agreed, the dive outfits there are not only very professional but diving there is a lot less hurried than with Singaporean dive operators. After diving with both kinds for years, I can say that generally, when you dive with a Malaysian operator, it's the quality of the dives that is essential, whereas when you dive with a Singapore-based dive company, you'll find you're being rushed through the day, because they whisk you off from one spot to the next in a blur, keeping up the chop-chop tempo all the while.
So if you're into padding up your logbook and ticking off dives, then go for a Singaporean outfit. If, on the other hand, you feel that diving should be a fun leisurely activity that you drink in at your own pace and you prefer to really relish each diving experience, then go with a Malaysian operator.