Pool at the HIlton is bigger, comes with a better view and 2 hot tubs vs. the one at Conrad. Pool service is pretty good at both but seems to be a younger crowd at the Hilton. The HIlton has 2 restaurants on site and their breakfast options are better than the Conrad in my opinion. You are correct in that upgrades at either property are rare for Diamond so book the room you want to stay in. Hilton rooms were renovated over the past few years and Conrad is still fairly new.