If staying onsite and on a budget, Universal value room wise is much more economical. My 20 / 30 somethings did a week long Universal trip for the opening of Epic Universe and really enjoyed themselves. They stayed at one of the new value resorts.
Now me (and note that I turn 65 in August) as much as I think the Harry Potter theming at the Universal parks is cool, I am more of a Disney girl. I just don't care for simulator rides and all the Universal parks just have so many of those. So for me Universal -- I've been three times - is not a park I plan to go back to. I wouldn't mind maybe trying Volcano Bay, the water park. I'm not doing Disney as much these days either, but given the choice between the two I am a Disney girl if I am planning the vacation and paying for it. I can't stomach Disney's onsite prices though and stay offsite when I go, but I hate it that as an offsite visitor I no longer get rope drop. So I do understand now why so many might cough up for Disney onsite prices. I can't do that though with my bean counter personality lol.
My next two big vacations are national / state park based vs. theme park based. I do though love both national parks and theme parks. Both are so much fun. And since I don't camp anymore, fly out, and rent minivans, the National Park trips are actually more expensive than the theme park trips.