Although I much prefer the NRT RCC to the one at HKG, I prefer to connect through HKG on my way TO SIN. My reasons are the shorter (and usually ligh load) last segment to SIN and the assurance of no bus ride to/from the plane at HKG!

When leaving SIN, I prefer the NRT connection and the NRT RCC lounge and showers.

Yes, HKG RCC has 1 or 2 functional showers now. I run from the plan to get one!