I would be happy in Row 7 E+ on way over at night if it came to it. The flight back is an hour + longer and it will drag in the day time. I know some people like to lay down over night but I actually prefer the bed on the way back. Night flight goes by in a flash.
Never a train to EDI from LHR. It doesn’t have direct train connectivity out of town like MAN or BHX. You have to schlep your bags into central LON on HEX and then the tube depending on station….and then it’s 5 hours riding. No way.