I agree, as it all depends on so many subjective factors.
My family has way more fun at Universal than at WDW these days -- mainly due to the smaller footprints of the parks making them easier to tour and to access in minutes from any onsite hotel, the higher quality and thrill level of the new attractions (if you compare what's new at each -- innovative coasters like Hagrid's and Velocicoaster at Universal's Islands of Adventure, and ho-hum dark ride copies MMRR and Ratatouille at WDW -- the difference is almost laughable), and the ability to breeze through the lines and enjoy unlimited express pass simply by booking a premier hotel room (for no more money than a Disney deluxe would cost and in many cases far less, and no need to purchase add-on crap like Genie+ and ILL, or to have your nose in your phone at any point).
That being said, I still rate Magic Kingdom as the "best park" overall, based on a lot of intangibles like nostalgia, vibe, a pleasing layout and thoughtful design second to none, and the sheer variety and quality of attractions. If theming and immersion become the primary factor, then Animal Kingdom also shoots toward the top of the list, as well.
Hollywood Studios and Epcot (at its present-and-for-the-last-few-years-state, with half of the erstwhile Future World overtaken by an ugly and unnecessarily-prolonged construction zone) easily occupy the bottom of the list, with each offering a small number of attractions that is completely disproportionate to their huge and inconvenient footprints, and increasingly schizophrenic theming and park identity. I'd put Universal Studios Florida alongside them, as it suffers from over-reliance on screens and redundant ride systems (e.g., Fast&Furious is an inferior copy of Kong, and Transformers and Spider Man are each basically the same ride with different video footage), and some discordant theming issues, although at least it offers a more walkable footprint, and is part of a property that offers more touring advantages and amenities for onsite guests, overall, than WDW does.