PNG has some fantastic diving and really healthy reefs. Most of the divers I have meet who have dived the Maldives have been underwhelmed by the diving - it was affected by a bleaching event a while back, but has apparently recovered.
My own observation, from a very small sample population, is that divers who do like the Maldives haven’t visited better SE Asian/Micronesian sites – but hopefully I can be proved wrong in this thread.
Liveaboards are the best way to dive: nothing but sleep, dive, eat, dive, eat, dive, eat, dive, drink and sleep repeated for days on end. That’s of course if you can stomach it (you can still do PNG/Sulawasi by live aboard if you so desire...). Most are quite large and stable and there are drugs you can take that may help you- but for the quality of diving I personally would do PNG a few times before the Maldives.
Cheers,
Rohan.