We've done both. MVMCP is a lot of fun for the kids - great special fireworks, treats, parades. It's a big event, fun to run around at a time when the park can't be overrun with crowds too. I took my boyfriend to the Star Wars Dessert party and we really enjoyed it. The specialized desserts, the Chewbacca stein, the creativity with the food was amazing, and the fact that it's all you can eat and drink, even an open bar, feels pretty decadent. But you are herded to a special area, of course good viewpoint for the fireworks, but it's short and maybe not a thrill a minute thing for the kiddies. And it's totally focused on the fireworks - at the same time there was a dance party going on just across the way - which was loud and had characters and would have been fun to go over and enjoy but it felt like we should be standing around waiting in the roped off area for the fireworks -- a little weird.
Hope some of those details helped you... If I had to choose for myself, top would be the Villains Club (you didn't mention that but if you ever have the opportunity, that blows the other two away! Then the Star Wars Dessert Party and then MVMCP. But if it was for the kiddies, MVMCP, The Villains Club, then the Star Wars Dessert Party