Thanks for everyone on the opinion of overnight sleeper on seated seats.
I did the Megabus M11 last year and it was not fun... No service breaks and the air con was on all night blowing freezing air. I thought the train would be better as least you would have a decent toilet to use and it's a bit faster, but no good if the air vent blows cold air and if the window views are restricted by a light above the windows
One advantage of the coach is they dim the lights .