Well, for reasons of time and money, I haven't been to most of them (just one), so for me it's more of a wish list! If I won the lottery and enough time went by, here's what I'd target and why.
1.) Papua, New Guinea. I hope to be blessed with a trip to Raja Ampat someday since it seems more practical, but from researching on the forum, I get the impression that for tropical coral reef diving, Raja Ampat edges out Komodo (not trying to start a fight here...) and PNG equals or edges out RA, plus PNG has WW2 wrecks. So does the Solomon Islands.
So, by explanation and reputation, I'd aim for PNG as arguably (there will always be argument) the (or amongst the) best tropical coral reef diving on Earth.
2.) The Galapagos Islands - I've been. Very nice; my complaint is I wish the viz. was much better so I could better appreciate and photograph the life teeming in the waters. I wasn't there in whale shark season; still haven't seen one. The topside, the 'household name' recognition, the strong historical role of the Galapagos...I don't think Cocos Island or Socorros (neither of which I've been to) match that. Cocos Island has tiger sharks (you decide if that's a pro. or a con.), but I've dove with tiger sharks out of Jupiter, FL with Emerald Charter, so I wasn't looking for them here.
3.) Guadalupe, Mexico. We can argue whether hanging out in scuba gear in a cage in a 'reverse zoo' situation is 'diving,' but close encounters with multiple great white sharks in good viz., hopefully taking snap shots of epic scenes of horrific primordial majesty? How does that
not make the list?
4.) Komodo, Indonesia. More drift diving, billed as great but not quite up there with Raja Ampat, but...the chance to walk topside in the domain of the Komodo dragon. Another one of those 'household word' name recognization destinations. A neat place to tell your kid you've been.
5.) Tie between the Red Sea and Australia's Great Barrier Reef. This would get down to topside comparisons. Both have a rep. for great diving...that you can beat at other places. Both have pretty strong name recognition and it's my understanding are best done by live-aboard. If we remove cost as a factor, then topside excursions come into play. If you could go on a river tour and watch salt-water crocodiles lunge out of the water for food close to you, or ride a camel in front of the Pyramids, what's your preference?
This is a very subjective list. I view wrecks as artificial reefs; I'm not a big history buff. So Truk Lagoon doesn't call to me. I have no technical diving training or credentials, so seeking to dive with coelacanths or some other off-the-wall extreme 'ends of the Earth' experience isn't in the cards. I'm not claustrophobic but cave or ice diving? No! I had one trip to enjoy California diving with kelp, harbor seals and California sea lions; kelp rocks!
So my priorities focus on tropical coral reef diving and/or big animals as a solo dive traveler willing to do live-aboards. If someone's rolling in money with luxury-loving non-divers to entertain, I've read good things about
Wakatobi (emphasis on
read; I'm not paying for that!!!).