Universal onsite hotels are priced somewhere between WDW's Moderate and Deluxe Resorts. The Hard Rock and Royal Pacific are within walking distance of the parks but all 3 hotels offer a boat service as well.
The 3 onsite hotels have the best onsite perk offered at any theme park: unlimited Fast Passes. The exceptions are Harry Potter's Forbidden Journey and the Rip, Ride, Rockit roller coaster. For FJ, you'll get a one-hour early admission into WWOHP.
You also get preferred seating at the restaurants, meaning they'll seat you ahead of other walk-ins.
The 3 onsite Universal hotels are really nice, as good as WDW's Deluxe Resorts. For the onsite perks alone, and the convenience of being able to walk to the parks, I suggest you stay 2 nights (or longer if you want to) at a Universal hotel.