I would say without a doubt Portofino is the best hotel in the Resort. It has the best theme, food,space, pools, and feel of any of the hotels. It is such a great place to relax and unwind after a day at the parks. They are in the process of renovation, which means that the rooms are being slightly modernized and the facades are being spruced up. The piazza overlooking the bay is very scenic and a perfect backdrop for dinner or a drink at one of the restaurants at the hotel.
Hard Rock is my second favorite of the hotels. It is located right next to Universal, and is often cheaper than Portofino. Personally, I am not as into rock and the like so the theme doesn't quite suit me, but for those who are into that Hard Rock is a great option. The rooms are a little smaller and not as nice as Portofino, but they are still above average.
I've only stayed at Royal Pacific Twice so I do not have as much to say about it, but it is a pleasant place that is more like Portofino in terms of it's laid back atmosphere. It is also the closest hotel to Islands of Adventure, which is a benefit to those who love that park.
Overall, you can't go wrong with any of the hotels on Universal's property. If you have the money and are willing to be relatively far from the parks, Portofino is the best choice.