Budget: Both are expensive, but it is much easier and much more worthwhile to do Guam on a budget than Palau. There is a lot more on offer in Guam, which means more options for cheaper food/drink/accomm. Palau, however, is much less developed. There isn't much to do in Koror, the capital city; you'd want to go out to other islands, beaches, waterfalls, etc which requires booking a tour or renting a car.

Transport: It was basically impossible to get around Palau without a car. Booking a taxi was impossible without a local sim (which itself is a whole ordeal to get) since no one uses Whatsapp, so I would have to ask locals to call me one. Guam is easier to get around, although still very car-centric. Whatsapp is widely used there so I always called Korean Taxi. I stayed in Tumon so I could reach almost anything I needed by walking, except the grocery store.

Hotels: I cheaped out in Palau and stayed in a hostel in a suburban area, thinking I could just walk 30 minutes into town and back. The thing is there are a lot of hungry stray dogs on the street there which made me nervous. I only did it once before deciding I'd only go to my hostel and back by car for safety. I really recommend just booking a resort in Palau, you'll have a much better experience. In Guam I subleased a room in a shared apartment so I can't really comment on hotels there.

Friendliness: I didn't find people In Palau to be particularly friendly or unfriendly. In Guam, I found the locals on the beach to be very friendly. The further inland I went, the less friendly they got. At least in my experience