hi,
you could get some really nice pics in palau. with an abundant source of subject matter from sea fans and soft corals to sharks and rays, it is tops. if you are interested in cavern images there is a easy dive just off sams tours called chandelier caverns. last week the highpoint of our trip was a spotted eagle ray just hovering at new drop off the whole time. if that weren’t enough, a hammerhead shark showed up for a pass or two.
yap has the famed manta rays and some decent wall diving. the dive operation at yap divers could use a little polish on customer service skills but otherwise a good time. a special dive in yap is the mandarinfish dive done at dusk. lots of staghorn corals populated by 30-40 mandarinfish each. the best part is the depth...5-10 feet. so, one could burn a tank for about 2.5 hours and swaping out memory cards.
guam has diving but pales in comparison to yap or palau.
chuuk is another great spot in the south pacific. going myself soon. the entire site is wreck dives from WWII operation sinking japanese fleet. lots of nudibranchs from what i hear. also lots of wreckage intact inside the cargo holds.