Seattle. I got free premium economy status upgrades every flight, but I'd check the seat map during boarding and head straight for an empty row, if there were any (and there often are on those routes). If I felt any risk at all, I'd actually switch seats in the app.  

Business class is best, but a whole row definitely beats premium economy. Actually sleeping is so precious on a red-eye, the difference between a miserable first day and a productive one.