To begin with: I've only been to Galápagos so far but what you can see there (already in central Galápagos) is amazing. Choose a good diveshop (I recommend the one opposite of Hotel Silberstein in Puerto Ayora on Santa Cruz) and go to all the nice places. I've had schools of eagle rays in "El canal" - that was after the sealions playing around with us, the huuuuge porcupine, some white tip reefsharks and of course as many turtles as you may have never seen before in ONE dive. If you're lucky you'll also see a hammerhead there. Otherwise there is Daphne Minor which is great with some sharks (silky, Galápagos-shark, hammerhead), mantas and turtles again or the famous Gordon Rocks which are the one spot in the central Galápagos where you're almost guaranteed to see small schools of hammerheads (up to 20) in one go. If you have time and budget I would definitely recommend a liveaboard-trip up to Darwin and Wolf since this is where you get to see whale sharks on every dive (in Darwin) and schools of hammerheads in 200-300 animals... besides huuuuge tunas in schools, sharks and all the funny stuff ;-) Unfortunately I did not bring my photo-camera last time I was there so I only made pictures from above water. You can find them on my page in different subgalleries.
That is what I have experienced last year. This year I'll go again with my photo camera and get a shot of a hammerhead swimming right over my head :-) (since it didn't see me before swimming over the rock I was waiting behind because of the strong current).
For those that have been to both destinations or just one I would love to hear your input! I would love to do both but I dont think I can squeeze them into the travel budget!
I love all marine and wildlife but the big stuff has always attracted my eye!
Love to hear any suggestions, companies, hotels, info from the water and topside.