We usually do 2 MK days and 1 day at each of the other parks, but this year we are skipping AK and doing 3 days at MK. We don't do full days, though- just until dinner, except for 1 night for Wishes (my kids are used to going to bed at 7).
On our departure day, we let the kids choose which park to return to and they always pick HS to do TSMM again (I book fastpasses for it because I'm 90% sure they'll pick it every time and if not, I can change them).