Hawaii? Maui has pretty much everything, except for active volcanoes. Staying on the west side of Maui, and driving up Haleakala and around on the road to Hana is pretty good. But if you have time, or you particularly want to see volcanic activity, you need to also go to the big island. I preferred staying in Hilo, but that is just because I prefer rainforest to desert.
As for Guam, it came across as a cross between Hawaii and Puerto Rico, and with a large military presence. As you might guess, Saipan, Tinian, Guam, and Yap were a single trip. I found the people in Guam and Saipan very friendly -- I think they were glad to see a tourist from the 50 states rather than the usual Japanese tourists. Tinian was mostly about the remains of a massive WWII airbase, including the bomb-loading pits used for Enola Gay and Bocks Car.
Yap is mostly about the stone money and diving. Also, a significant fraction of the people still keep to traditional clothing, so at the airport a couple of topless teenage girls welcome you to the island. This was almost 10 years ago, though.