I guess for no other reason than it's our favorite, we always went to Epcot right after arriving, and still do, sort of. When we made advance dinner reservations we would plan around those for which parks we would go to, but would often just go where we felt like at the moment, sometimes even getting on the first bus that came along and then moving to where we had dinner reservations later in the day.
We started going to WDW 20 years ago and really structured our days for the first 8-10 years. Since then, we enjoy going with the mood and a more relaxed schedule. What we don't get to do we can always do another time.
Now that we live just over an hour away, we still just go with the mood of the moment, but still like Epcot the most. We still stay at an onsite resort for several days now and then because that was always a big part of the experience.
We have never been to WDW the time of year you are going, so I have no first-hand knowledge of crowds that time of year, but Epcot is usually the easiest for dealing with heavy crowds since there is more room to spread out. The Magic Kingdom is a more shoulder-to-shoulder experience when crowded.
I would suggest making dinner reservations at your favorite restaurants and working the parks around that. If reservations are difficult to get for the restaurants in the parks, try the resorts. The deluxe resorts have some of the best restaurants in WDW.