Stayed in Belmond a few years back. Was in the same position, got a good rate at Belmond and Rosewood was pretty new so went with Belmond
You've basically nailed the pros/cons from what i see. Good view, good spa/facilities. Service was off. Food was not good. I think we preferred our more modest hotel in town.
I'd probably suggest Rosewood
check out Manda de laos for dinner.