Just came back from Hollywood Studios and while I can't comment on how much my 5 year old would have liked Universal, he absolutely loved HS. Between meeting the Power Rangers and Lightning McQueen / Mater for pictures, sitting through the Indiana Jones show, and the new stunt show (best of all!) he can's stop talking about it. The stunt show alone may be worth the price of admission (well, maybe not that much, but you know what I mean.)
Disney Playhouse was also a big hit so he really had a great time. He actually liked it even better than MK. Just FYI, we were there Tue. (MK) and Wed (HS) and we were there for rope drop on both days. By 2:00, the crowds in both parks but especially MK, were unreal. Hardly had room to move through FrontierLand.