Open-close, getting there BEFORE rope drop and lingering in the parks as long as possible after closing!
Even when there as a "seasonal resident", I still love my open to close rope drop days!
Since I consider all 4 parks "full day" parks, I never run out of things to do at the park I started at, and never get bored. When the park I do "open to close" at closes, I like to park hop to another open park (usually MK) until that park closes. I park hop to Disney after a full day at Sea World and Busch Gardens as well, as MK and sometimes Epcot usually have later hours.
My "record" for longest single-day park hop was visiting Wild Adventures in Valdosta Georgia, which closed at 8 or 9 PM during their December Christmas event. On my drive to WDW, I did an open-close at Wild Adventures, and drove the approximately 200 miles to WDW, making it into MK before the 1 AM closing!
If I am doing a "full day" at a park, I like to get there for the Welcome Show/Rope Drop, or else I feel like I missed something, like missing the first scene in a movie or first song on an album. I love the feeling of "opening the park" and seeing it come to life, getting a "walk-on" on my first several attractions of the day.
And I also love the nightime atmosphere of the parks, seeing the uncrowded SECOND MK night parade, and getting walk-ons on attractions right before closing!
If I am tired after multiple full days and need more sleep, or don't have the full day available, I don't mind sometimes doing an evening visit starting at around 6 PM. These feel more like a park-hop, and there is no pretention of having a "complete" visit. So I see the fireworks, parade, and a few favorites.
And I think that hits on why I still like to do full days, even when I lived in the area seasonally. When I do short visits, I always tend to gravitate to my favorites, skipping my second and third tier of attractions that I still enjoy. Full days give me time to give my second and third tier attractions some visits on a regular basis.
As far as half-days or partial days, I am much more likely to do a half-day in the second half of the day, because once I open a park in the morning, I NEVER want to leave! (although I have done so occasionally due to special events I wanted to experience happening at two parks on the same day).
I know a lot of people get tired doing full days and like to take a midday break. I guess I'm lucky in that this rarely happens to me, and when it does, I find taking a short nap in one of the air-conditioned indoor theatres usually does the trick and gives me a second wind, and is much easier than leaving the park and coming back.