West Coast, has the most interesting scenery and most comfortable trains, as the Class 390, 805, 810 and most of the class 350’s are very comfortable. Scenery is very impressive north of Lancaster, particularly if you like looking at hills. South of Lancaster it is less interesting, but still more interesting than the East Coast line south of Darlington. For some reason it feels faster than the East Coast and Great Western Mainlines. However it is let down by poor reliability, it is unusual for an Avanti train to arrive on time, though the London Northwestern trains seem to be better.
Great Western. I have not travelled west of Didcot for some time on this line, however I do not rate this line that highly. GWR’s class 800, 801 and 802 trains are really uncomfortable and have no buffet, which I think is poor given some journeys are plus five hours. Scenery wise, at least on the line proper is not that interesting and reliability is poor. Travelling east into London, I find it is very unusual to arrive on time. Furthermore, the frequent stops are frustrating.
Great Eastern, has comfortable trains, with the class 745 having good seating and even a buffet, which is good going given they serve journeys of less than two hours. Reliability is very good, however the scenery is really boring outside of London. Only interesting thing scenery wise is the approach into Stratford.
Midland, have not travelled on this line for several years so can’t really comment. Passing Radcliffe-on-Soar power station was interesting, but alas this has now closed.
East Coast. Great scenery north of Darlington if sitting on the east side, particularly through Durham, Newcastle and around Berwick, however really boring scenery south of Darlington. Generally I find this line reasonably reliable. LNER’s class 800 and 801 trains are not that comfortable, though they are better than GWR’s as they have a buffet and Lumo’s trains are more comfortable.
Based on this, I would vote the West Coast first and Great Western last.