All options open, I would never take a middle seat. I prefer aisle, except PHX-SLC-SEA, which I fly frequently. Flights are short and I never get tired of the aerial view of that part of the country.

However, when options are limited: I have taken a middle seat on a WN flight that looked like it was going to be packed - better to grab a middle between two small people than risk something worse.

And I have taken an exit row middle when the aisle/window were taken. I prefer exit row middle to non-exit row aisle/window.