Animal Kingdom allows the most leisurely pace. It's also the largest park by far so there's a bit more options to escape the crowds other than some main pathways and so it's park capacity will also be high. Pandora does get busy but still typically should allow room to move. There you'll be occupying your time more with exploring trails, seeing animals and such with a few sprinkled attractions there. Satu'li Canteen however is my favorite QS place.
Epcot would be my second option. While World Showcase itself can get busy in terms of walking from attraction, show or pavilion and that is something to keep in mind, the pace is typically less frantic due to the nature of the attractions/shows, etc there and it seems to really help that there is no longer a split in when World Showcase opens with the front of the park. Remy however is prone to breaking down, obviously Test Track still encounters issues but that's not something new and usually you can still ride it at some point in the day. FEA can have issues but doesn't seem to be nearly as much as in the past. When we were there in May however the front of the park was a mess like it has been with the construction, it does make for a detour to get through to some attractions and World Showcase. Connections Cafe/Eatery at the front of the park appears to be a good QS location too, while we didn't get anything our DISer friends did. There are plenty of other QS options in Epcot but just thought to mention that because there is a ton of seating, if nothing else it's a good spot to catch some A/C lol. It was our meeting point for our Guardian preview and made for a quick way of finding each other.
Something also about Epcot is you can opt to escape the crowds (like we did although it wasn't super super crowded) is take the Skyliner from Epcot (you do have to hike to the back of the park through the throngs of people but still) to various places. We took it to Riviera to snag some coffee and sit in the lobby just relaxing and sorta taking a breather. That lobby also does have couches and chairs near charging sockets so we used those instead of draining our portable batteries. You can easily take a tour of the skyliner similar to monorail hopping. Our DISer friends did that before meeting us in Epcot.