I'd take almost any window over almost any middle. Unless worried about a connection, I'd take the window in the back.

Bulkhead seats are often narrower with tray tables in the armrests and don't always have a big legroom advantage. I've grown to *not* like bulkheads, unless it's a type/airline where I know the footspace is fully open. (AS E-175 seat 6B, for example.)

The point about upgrading is a good one though: take your window in the back, but keep watching the seatmap around the times that elite upgrades are processing. And then check it every couple hours in the day leading up to your flight.