Not a whole lot of difference, at least on paper. You'll have express pass with both and early admission to the parks with both. Portofino is technically in a higher class, but with only one night, you probably won't have much time to take advantage of the amenities. Royal Pacific may be a little closer to the parks, but not by a lot.
I'd say check them both out online and see if one jumps out as being preferable in theming, location, etc. For your length of stay, I think you'd be happy at either.