It's been ten years since I've been there, but I recommend Sam's for diving and the Carolines for lodging.
The two islands the US captured, Peleliu and Angaur, were at the southern end of the archipelago, but the Japanese had a massive base at Koror at the northern end of the chain. Koror was the capital of Japan’s Pacific holdings and was one of their most secure holdings in the Pacific. After the losses from Angaur and Peleliu, the US scratched all plans to invade Koror, but a massive air battle was waged from August 1944 to August 1945, and saw the loss of over two hundred American aircraft. Half of these aircraft were lost outside the lagoon (in water a couple of thousand meters deep), but there were still about 100 planes went down either over land or in the lagoon. Only about half of the crews survived.