I can't comment on the hotels being discussed but if you haven't been to Bali before I think you should stay in Ubud - you may disappointed in Balinese beaches if your handle gives any clues to where you live. I hate black sand beaches - too hot and not attractive to look at and the area where Amanusa is is just an enclave of 4 and 5 star hotels far removed from anything Balinese.

So Mandapa looks like the best choice - may even try it myself next time we visit if the reviews are that good.