You will find that everyone has their favorite, but I think that just means that all of them are quite good. Of the two mentioned, Sams is probably the biggest operator in Palau and Palau Dive Adventures is one of the smaller ones. Sam's has its own restaurant, bar and Yacht Club. Palau Dive Adventures is just a small shop adjacent to the Sea Passion Hotel. The two of them, plus Neco Marine are all within walking distances of each other. The other operator that is often mentioned is Fish N Fins. It is a ways from the other operators. Fish N Fins has two liveaboards and Sams is partnered up with the Siren fleet, plus two private charters. All of the operators have hotel packages.