We have stayed at HRH, RPR and CB. My son would pick HRH if given the choice. (He is 18 now). The vibe is cool, the lobby is cool, the pool is cool, lots of teens (read "girls"), and so close to the parks. I know lots of people here don't like the way the rooms look, but we always have, and that is before the rehab.
How many parks days depends on how you like to spend time in parks. My son- who brings a friend- likes to re-ride. Like ride the Mummy 10 times in a row using the ep (hence the need to bring a friend). So it might take longer for us to get through a park since we are big into re-riding. My husband likes to take frequent breaks (bad back), and I like to slowly peruse every little detail of the theming. So how many days in parks depends on what you like to do in the parks.
Staying on-site at Universal makes for a very different trip, so you can tour differently there than how you tour at WDW. The ep's change everything. You can tour leisurely, re-ride as many times as you like, walk back to your very close resort and relax or swim if you like for a break then quickly and easily get back to parks, and for most part not wait in long lines (except for some of the HP stuff).
My suggestion would be to try to take advantage of touring UO style. Leisurely and with as many repeats as you like- because you can.