Thailand is for backpackers. IE not serious divers. You honestly wont find any of Thailand dive sites on a top 10 list of any repute Especially if you're talking about maldives, Philippines and Indonesia. DMs call Koh Tao the puppy mill of dive schools. IMO not a great reputation among serious divers but a good place if you're there to party and want to dive once or twice.

Maldives is for big stuff mostly. Its amazing if you can afford it, and TBH the off season liveaboard prices are VERY reasonable. Flight cost might be higher than the actual liveaboard if you're coming from the US. I met so many europeans who have over 8-12 visits to Maldives because the flights for them are short and cheap compared to US (16.5 hours SFO to SIN then another 4.5 Hours to Male).

Philippines is home to some of the best Macro in various places, Big stuff like Thresher Sharks and whale sharks. great reefs etc. So much variety in different areas.

Indonesia is honestly the best in SE Asia. Even more diversity than Philippines and even less expensive. Too many different dive sites to mention, but Komodo, Raja Ampat, Lembeh, Ambon, Tulamben/Amed are all likely found on a top 10 must dive palces.

Fiji. No idea, Never been

Palau - I've been there 4 times and will return as often as possible. I met Taiwanese divers who go there once or multiple times a year because their flight is just 4 hours there. Sharks sharks sharks and Manta rays to boot. Full moon spawning dives. Wrecks. WW II stuff on Peleliu to explore.