Having stayed at both many times, another vote for Hard Rock but I think it depends on your interests. Portofino is much more relaxing and therapeutic while Hard Rock is high energy. Plus, I love loud classic rock music!
We stayed at Portofino last week. The boat service was excellent. We always just walked on.
We enjoyed Sal's and Mama Della's with no reservations and no wait.
The walk wasn't bad in the April weather either.
Upgraded to deluxe room with semi'private patio, so nice for a family of 5
We did eat at the Hard Rock and liked it.
We've stayed at both, and it depends on what you like. I would choose PBH because it quieter, more beautiful IMO, and further away from the action. The boat ride to the parks is just fine / easy to access. If your desire is to be within walking distance, then HRH is a no brainer - but it can get a little boisterous at times. If that's OK with you / then great. Either is not a bad choice IMO.
I consider the PBH to still be within walking distance, although it is farther. I think the last time I timed it, it took us 11 minutes to walk - with a stroller - from the PBH boat dock to the security checkpoint right next to the Studios entrance. If we aren't getting on the next boat, we walk.