Having stayed at both (and returning to both this year), it really depends on what you and your family prefer.
If being the closest to the parks as possible is a factor, then Hard Rock is the closest hotel of them all.
If the pool is a factor, Hard Rock has a pool with underwater speakers and one of the zippier waterslides on property. Royal Pacific has a nice big pool with a sandy beach, and while it doesn't have a waterslide, it does have a little ship sprayground.
If you prefer a laid back vibe, Royal Pacific does that a tad better for me.
For food, personally for me, Royal Pacific does a better breakfast. Can't really comment on lunch or dinner since I've always eaten in CityWalk and the parks for those. Royal Pacific also recently opened a new grab n' go spot, which could be more substantial than the one that Hard Rock has. Conversely, for something high-end, Hard Rock has the Palm steakhouse which I've heard nothing but good things from.
In all honesty, both hotels are really nice no matter how you pick em'.