What mode of transportation would be the most scenic?
It doesn't make a lot of difference as the road and rail routes are basically the same. The difference is that the buses are more frequent- hourly- and the same schedule 7 days a week, take not much longer, and are very often (not always) double deckers.
Thus intrinsically better views if you are upstairs.
The bus is also normally cheaper than the train if you book through Megabus, as opposed to Citylink, on this code/share service.
You pays your money and takes your choice.
Thanks for your input!