kutchyone,
I will try my best to share my insights. Still it all comes down to personal preference. WE just returned from staying at both.
1. Price differences:
well depending on when you travel what rate you are able to obtain and the room type you desire will all make a difference. Overall you should be able to book Hard Rock at a lesser rate. I believe rock bottom rates are $117 Hard Rock Garden View and $160 Garden view Portofino.Room service is a tiny bit cheaper at Hard Rock and so is the bottled water..$1 less at Hard Rock.
2. Locations:
Hard Rock is easier to (quicker) walk to Universal than Portofino but I have no problem taking the boat ride from Portofino to even consider this when choosing.
3.Room size, decor:
Portofino's rooms are larger. Hard Rocks are more than spacious enough however. I like the beds better at Portofino. I liked the decor in both hotels. We found the TV's to be bigger at Portofino if that even matters.
4.Pools:
Tough one for me...I love them both. My husband likes Hard Rocks better. My son enjoyed both slides very much. My little guy (4) liked the Portofino pool area better cause they had a pirate ship play area. But he loved the spraying fountains at Hard Rock.Hard Rocks pool area is busier and more lively. Portofino's is more sedate. The bar service at both were great. Portofinos food service at pool area is closed not sure when its due to reopen.Nightime swimming for some reason was enjoyed more at Hard Rock along with thier jacuzzis. Hard Rocks pool is larger.
Eating Facilites:
As much as we loved the trattoria at Portofino we loved Sunset Grill better at Hard Rock. People are more fun and food is prepared to perfection with wonderful choices for all. Service was outstanding. Had bad service for breakfast one morning at Trattoria but they handled it immediately and removed the meals from the bill. I like the different choices at Portofino and felt in a rut at Hard Rock easily solved by eating at City Walk though. Hard Rock has Sunset Grille and the outdoor Beach club and a steak house The Palm...If it rains (pours storms) you arent going to want to eat at the Beach Club. That left us with only one alternative or room service...since we would not eat at the Palm. It is also very expensive. Portofino has a few more eating options there is the Trattoria open for breakfast lunch and dinner...Mama Della's really good Italian food not too expensive and family style.Sals an Italian deli that offers pizza's as well. (we always eat here at least once) you can also take it back to room or order it from room.Splendido Pizzeria overlooks the pool. The Gelateria for pastries ice cream and specialty coffees. I frequented there daily sometimes twice

Also the room service menu. Delfino Riviera only open tue-sat dinner only...expensive and elegant. Character meals are offered at both hotels Mon and fri at Portofino and tues and saturday at Hard Rock.
6.Discount Possibilites:
Same type discounts offered at both but untimately you will pay more for a room at Portofino. Try
AAA, Entertainment rate, Loews,Fanclub and Annual Pass for discounts.Also occasionaly Universal offeres some packages that are pay for 3 days get fourth free and they are decent deals.
7.Family Oriented:
How old are your kids? Mine are 4 and 8 and they enjoyed both hotels. They both catered to the family. Portofino has a more european flavor where Hard Rock is just cool and carefree. Both were great for families.
Our family love both so we'll keep trying to frequent both

Good Luck and have fun planning.