Personal experience: I have visited Palau twice in 2017 and 2018. I was impressed.
Beautiful Palau claims to have 84% of it's rainforest cover still intact....
Palau is a small nation made of just a few small islands. The main island group is made of uplifted limestone which forms a stunning network of islands, bays and reefs. Some of the islands are connected by various bridges.
There are some interesting birds to be seen around Palau. First, there are many seabirds to be seen easily in and around the islands and waters. They include white-tailed Tropicbird, Bridled Tern, White-capped (Black) Noddy, White (Fairy) Tern, and Black-naped Tern. The land based birds include many species endemic to Micronesia: Micronesia Starling, and Micronesia Myzomela.
There are some interesting reptiles. Most of the ones I saw were widespread species, including Hawksbill Turtle, and Yellow-lipped Sea Krait.
I didn't expect to see many native mammals in Palau, because there aren't many. However, the 'Pelew Flying Fox' seemed fairly common. Just watch out it doesn't end up in your soup (a traditional Micronesian meal).
Palau is a tiny country in the middle of nowhere! There are flights, but they will always go via somewhere else, and it is a long way to go. Be aware that the jellyfish lake is still closed (as of 2018). Some of the expedition ships, such as Silver Discoverer (with Silver Sea) go there. That is who I went with, as a guide/lecturer.
Most of my stay was based just around the Palau Royal Resort. This is probably a fairly pricey hotel (but I didn't pay as I was accompanying a group). I photographed many of the species on this page there, and you can also snorkel right in front of the hotel.