Best PHP locations for experienced diver + non-diver?

[Centrals]

True enough about the crowds. We'd prefer something more Koh Lanta and less Koh Samui if that makes sense? Trying to avoid situations where there are 25 divers following the same sea turtle.

South Leyte(Sogod Bay) is even more quieter than Koh Lanta and dive sites are much much more closer. The only issue is getting there but that is the saving grace for the place.
Koh Lanta is not that straight forward to get to if you are landing at Bangkok or even Phuket in late afternoon.
Peters is also my suggestion.