Fastpasses and ADRs actually don't play into how we decide on what park to go to at all because we don't have any do or die attractions or restaurants to schedule.
Also, we park hop, so that allows us to go to more than one park per day, which we often opt to do.
Before the hours are ever even announced, we make a preliminary schedule based on our own preferences and and any special events. Like for our next trip we'll be buying tickets for
MNSSHP, and we prefer to go to that on a Tuesday, so we will mark Tuesday as an all day MK day.
My kids like the water parks, so since we'll likely be tired after being at MK all darn day Tuesday, I'll schedule a water park for Wednesday morning, allowing us to sleep in a bit since those parks open a bit later, plus they're more laid back once you get there, too. Nothing eases sore feet like a few hours of drifting around a lazy river.
We like to break AK into 2 days, one morning, and one evening. So we'll stick AK after the water park on Wednesday and let that be our evening day there.
The day we leave is always our Disney Springs day, so for our next trip, that will be a Saturday.
And so on and so forth. If we've heard or experienced ourselves that some parks are crazier on certain days of the week, we'll try to work around that. And we will split days based on extra magic hours. If HS has early hours, for instance, then we'll go early on, but then leave for a resort break and go someplace else later...typically Epcot. Then another day we'll go back to HS in the evening.