We did MK our last day and loved it.
Since we already did MK during our stay, it was a more relaxed time:
Had breakfast at the plaza restaurant, took some pictures in front of the purple wall, did the people mover... noticed there was only a 20 minute wait for space mountain so went on it one last time... did a bunch of shopping, and one last Dole whip before leaving.
I agree with philbrody... probably depends what park is closest to you. We were staying at the WL, so getting to and from MK was pretty quick.
Right now, I wouldn't do Epcot because of the construction.
Galaxy's Edge in HS has some cool merch... that might be a good place for a last day. We always need to pick up souvenirs for family members on our last day.
Unless you're staying at AKL, AK would probably be the lowest on my list... to much travel time and I'm always exhausted with all the walking required there.