Window Seat in Economy or Middle Aisle Seat in Comfort+

Hello! I am flying to Frankfurt out of ATL on Monday. There is an upgrade to comfort plus available for $75 to an aisle seat in the middle of the plane (rest of the seats in the row are currently empty as well).

I’ve only ever flown economy and I currently have a window seat (45f🙃). Wondering if upgrading to a potentially empty row of 4 is better than a window seat? Is it worth it? I read once you upgrade you can’t do it again. I’m considering trying the “rejection therapy” tactic and just asking for an upgrade at the gate. Worth a shot?🤣

Just looking for opinions or someone who has experience with either! Oh and if it helps I don’t plan to have a carryon, just my backpack and purse. Cheers