We really enjoy both. I'll answer the question this way, in case there is a nugget of information in there somewhere that can help you...
Things we like better about the Hard Rock:
Proximity to the parks (especially USF.) You can't beat that super short walk, you leave the hotel and suddenly you are there.
The pool area. The underwater music, the way cool water slide, the pool bar set up. It gets the nod over RPR.
The room size, which seems a good bit bigger than RPR.
Things we like better about the Royal Pacific:
The theme. While HRH is definitely cool, we enjoy the South Pacific theme, the marvelous lobby garden atrium and the walk into the front entrance over the bridge.
The view. We've had great luck getting very goo IOA views. It's neat to see everything lit up and so close to your room at night.
We've found the service level at both hotels to be outstanding and it is very tough to leave either one for home. We tend to alternate stays between the two, but RPR gets a few more trips from us (mostly because of the price.)
Hope some of this helps