Let me preface this by saying that we don't do park trips when crowds are that high. Next month, we will be going to WDW and doing various activities outside the parks because they will be more crowded than we like. That said, if we absolutely could not go on park trips during the slow times, we would hit the parks during the busy times. So knowing that, I'm going to answer what our family would do.
If all of the parks were going to be crazy crowded like 10/10, we would not go to DHS. It is easily my favorite park, I can do all of the rides there multiple times without ever getting bored, love Fantasmic and the other shows, and think it has some of the best table service dining options (Sci Fi is the best themed restaurant in all of the parks, bar none, in my opinion). However, with a really high crowd, I would be standing in lines a LONG time. Tower of Terror's line is entertaining and all that, but I don't think there is a single line at Disney entertaining enough for me to stand in line an hour. I just think that DHS is one of the worst parks to be in when there are high crowds. You could Fast Pass Tower of Terror, Rock n Roller Coaster, and Star Tours for low waits on those, but then you'd still have long waits for Great Movie Ride and Toy Story Midway Mania and not be able to do the other three rides a second time without a high wait.
If it it a hot day, Animal Kingdom would also definitely be out. That park is hot. It is definitely the hottest park of the 4 and large crowds plus extra heat is not my idea of a good time. The park is easily my fourth favorite park to begin with and high crowds and heat will not put me in a good mood. Plus, I don't think there is as much good stuff to do here. After I would fast pass Everest, Safari, and Dinosaur, I'd be stuck with long waits on stuff that doesn't really interest me and then wandering around in the heat wondering why I ever thought AK was a good idea.
That leaves Epcot and Magic Kingdom. Magic Kingdom has so much fun stuff to do so it is one of the first parks I will visit if it is a really high crowd day. I can have fun at MK without going on the major rides like Space Mountain. Carousel of Progress, Tiki Room, Peoplemover, Country bears, and the treehouse are all attractions that I enjoy and usually don't have too much of a wait. Of course, on a 10/10 day, even those will have a wait, but they won't be ridiculously long like the wait for Splash Mountain will be. I'd fast pass three of my favorites (Splash Mountain, Space Mountain, Thunder Mountain), enjoy the queues for some of the other rides (Jungle Cruise, for example), and then do some of the lower crowd activities. I also love the ambiance at MK and can grab a Dole Whip and sit down in Adventureland listening to the music and people watching and still have a great time. Same thing with Main Street, Frontierland, or Tomorrowland. I can listen to Sonny Eclipse for an entire set and be content. So, Magic Kingdom is also really high on my list.
I find that Epcot lends itself to high crowds pretty well, too. I enjoy just strolling World Showcase, taking in some street acts, and enjoying myself. With FP+, I would still be guaranteed a ride on Soarin', Spaceship Earth, and something else and then could spend time strolling World Showcase. It'd probably be my second choice, but on some days I can see myself choosing it over Magic Kingdom.