How big are you and your travelling companions? Taller people might avoid Economy on Rouge, though the 767 used for TATL is reportedly better than the A320 series. Wider people might not like 9 across seating on an A310/A330 on Transat.

Being both tall and wide, I personally would avoid both unless I sat next to my youngest child on Transat. It's amazing how little width a skinny kid takes up. Or upgrade to a better seat. Maybe you should compare prices of the cheapest acceptable seat for each option. That's what I would do.

If you do an upgraded seat on only one leg, choose the overnight flight.