I live out here, so I can go to either Yap or Palau on moment's notice and without much planning. I've been to Yap three times, twice this year. I've only been to Palau twice. My next trip that direction is going to be to Yap again. I prefer the more relaxed diving atmosphere and culture of Yap. That and having mantas pass a few inches over my head. Again and again and again and again. Vertigo Wall beats the hell out of the Blue Corner for shark action, hands down. At Blue Corner, the sharks swim way out in front of you. At Vertigo, they swim into you. And there can be upwards of 50 of them. The diving in Palau is spectacular and not to be missed. But it can get pretty hectic, like when you dive the Blue Corner with 50 or more of your closest dive buddies. No problems diving on Yap on Sunday. I always do a manta dive the morning prior to departure (i.e. I dive Saturday prior to the Sunday morning flight). The manta station is at about 15 feet and I do it on Nitrox. Leaves plenty of time to off-gas. Personally, I'd add a few days to Yap. While it's still relatively unspoiled. BTW, my profile picture was taken on Yap a couple of months ago. That picture is uncropped and I wasn't zooming.