Totally agree that it would be impossible to choose one, even though I have only been to 6. We could, however, try to make a list of the favourite things at each of them, like I once did for FS. Mine would be (having been to jena, jiwo, dari, puri, wana and kila):
Best beach: puri
Best room: jiwo
Best excursions: jiwo - Private sunrise trip to Borobodur followed by elephant ride back to jiwo
Best cooking class: dari
Best food: indonesian feast at dari + Naoki at puri
Best arrival: water plane to wana
Best massage: puri
Best gym: puri
Best outside lounging: Bale at jiwo with view to Borobodur
Best bathroom: jiwo
Best snorkelling: wana
Best main pool: kila
Best beach "loungers": Bale at kila
Best complimentary in room snack: Dades at jena + fruit at jiwo
Best welcome: flower girls at jiwo
Best breakfast item: French toast at dari