There is no slide at RPH. There is an activity center which is a like a boat that has fountains and squirt guns to run through. My 10 and 6 year old sons had a blast at both pools, but they would tell you that the slide at HRH is way better.
As a guest at Universal Hotels, you can go to any of the Hotel's pools. So you could stay at RPH and go to the HRH pool.
I hope that helps,
Dad of Three.