We were going to go to Universal Studios but after much coaxing from my two daughters ages 6 and 10 we decided to go back to Disney and stay at the Poly Conceirge. I hope that we made the right decision. Any info on the Conceirge would be helpful!
As much as I love WDW, I think your daughters would also love the Universal Parks. Staying at one of their on-site hotels and getting the all day express access is a perk that can't be beat.
I would think that if you are doing all the parks in the Universal area you would stay in that area just for convenience sake. We spent a week at the Hard Rock Hotel last year and it was wonderful!
Our kids were 6 and 9 then and they loved the hotel. We used the onsite daycare for the first time ever and it was WONDERFUL!