We have been diving with several of the operations but by far our favorite is Pacific Rim. Patrice runs an excellent operation! She has a smaller boat (6 divers max) so everyone dives as a loose group. My DSLR was never a problem. They do not do afternoon dives (most ops don't) because the wind picks up and makes it kind of rough. But you get to dive your own profile so 70-75 minute dives are not usual. Plus she has homemade brownies every day!
Do not miss the manta night dive. Pacific Rim does not offer that so we use Kona Honu. They offer it as a 2 tank (reef, snack, mantas) or a one tank manta dive. Most all the operations take snorklers along too.
Schedule your dives and tours accordingly, some of the attractions like the observatory are over 14,000 feet.
I've been to both Yap and Palau a couple times - we just returned a couple weeks ago. While Yap is known for mantas there's a lot more to see. Primarily hard corals there while Palau has a nice mixture. The island itself is very laid back and friendly. Palau is a more diverse diving experience. I've done all my diving from livaboards so I can't comment on the land based diving.
If I could only do one I would pick Palau, but if you have the time the diving in Yap is definitely worth it!