In this new-ish century, I have largely switched for more-than-short journeys, from rail to National Express coach; feeling a bit of a traitor for doing so its just that in the main, coach proves a lot cheaper than rail: and Im not among the countrys more affluent inhabitants.
On the whole, I find rail travel more agreeable than coach; though thats not always 100% the case.
Various pros-and-cons: a PP mentioned the possibility on a train, of getting up and stretching ones legs. Regarding modern long-distance stock: Im one of those who perceive a tendency on the part of whoever designs these conveyances, to try to make train travel, resemble plane travel as much as possible hyper-narrow coach aisles, in various ways difficult and stressful to negotiate. When travelling long-distance by train nowadays, Im reluctant to leave my seat even to visit the loo. IMO present-day rail is, in this matter -- allowing for context -- no worse than road coach; but no better.
Coach-travel downsides for me: usually more time-consuming than rail. In the past few years, Ive been doing a good deal of travelling between Birmingham, where I live; and Exeter, where a relative to whom Im close, now lives. Rail time between the two, generally two-and-a-varied-amount, hours. Coach (scheduled) ditto, four-and-a-half-hours-plus. Greater amount of time by coach: because of time needed to get off / back on the motorway to access city / town-centre bus / coach stations, given the grappling with traffic to get into and out of said places. And, periodic half-hour / three-quarter-hour stops at motorway service stations, and / or city stops en route, to let passengers get refreshments / use the loo if they prefer not to brave the in-coach same / cover coach staffs necessary rest breaks. I personally can live with, and accommodate to, long time taken thus; but its not a thing which one would ideally choose. And Ive found that sometimes, National Express coach seats are not quite big enough for me not agonising discomfort, but not all that pleasant a thing that rail, overall, does better.
Coach pros: as said, mostly cheaper than rail, unless (in some cases) one books rail travel wildly far ahead often in my life, I dont know as far ahead as that, that Im going to wish to make the journey; and, taking it that you book in advance (as I do), youre guaranteed a seat, no messing. Ive never yet had a problem with National Express, regarding seat-booking / occupancy. On rail (with this being essentially a different ball-game) even if you reserve a seat, there is no certainty that someone will not steal same from you; resolving this, or failing to, being liable to lead to unpleasant and rancorous stuff in which if youre me even winning, can result in a miserable situation. And; in the great majority of my travelling with National Express, the staff have been very competent; and, even at their worst, OK to deal with.