Even in coach, train travel has the following advantages:
1) more comfortable seat (wider, softer, more recline, more leg room, a footrest),
2) baggage: free transport of carry-on and checked luggage that meets the standards--very generous, by airline rules.
3) freedom of movement: passengers are free to get up and move, use the toilets, seek food, go sit in the lounge car, etc. whenever they wish. Moreover, since the seats offer more leg room, you're not trapped in the middle of a section of narrow seats.
4) Food and drink: Most trains have a cafe/lounge car with excellent viewing and a variety of foods (from candy bars and chips to sandwiches and pizza slices they'll heat up in a microwave), drinks (including alcohol) plus useful sundries (aspirin, batteries, etc.) and the overnight ones also have a dining car where coach passengers can purchase meals. You can also bring your own.
5) Fewer weather delays. The day I left NYC, flight delays were predicted all over the Northeast and naturally that was expected to have an effect on flights in less weather-stricken areas, when their flight originated in the NE. My train left on time and arrived on time or early at all stops. Moreover, when a train originating in San Antonio was stopped because a track had washed out in a flash flood, Amtrak found buses, transported passengers and luggage to Fort Worth, where it had put together another train for them--they were somewhat late into St., Louis, but only 20 minutes late in Chicago. I've been delayed 10.5 hours between Austin and Chicago, during which time the airline showed no concern whatever for its stranded passengers (though alarm that we weren't being perfectly sweet and docile sheep.)
6) No overbooking problems. Airlines consistently overbook flights and deny passengers who have paid a fare the travel they paid for. I've been on full trains with Amtrak--but I always had my seat.
7) No "gate" delays: no sitting at the gate waiting for the assigned flight crew to come aboard (2 hours in one case, while the transfer time to my next flight whittled down), and no sitting on the runway for hours because "we can't find a gate open." When the train arrives, it's there. I have had to wait a few minutes when we arrived early, as they shuffled to get us a track, but it was never more than 5 minutes, and the arrival was still on time.
8) Scenery: see more of the country from track level than 25-35,000 feet. On all my trips this year, I've seen interesting and beautiful things I could not have seen from the road or from a plane.
9) Efficiency: Trains use less fuel per passenger than airliners, so if you're concerned about global warming (and you should be), a train creates less per trip.
10. Noise: Trains are quieter than airplanes. I always need my noise-canceling headphones in airplanes (but you can't turn them on until after takeoff...for some stupid reason) but don't in the train. If I have them on in the train, it's because I'm listening to music of my choice.
First-class/sleeper passengers have even more benefits (and first class on Amtrak is less expensive than first class on a plane):
1) The luggage allowance for sleeper passengers is generous; if you're traveling between stations where there's baggage service (requires station to be staffed for all arrivals), three bags can be checked per passenger--no fee.
2) Sleeper compartments offer a flat (not reclining: flat!) bunk for each passenger, complete with sheets, blanket, and pillow (no extra charge for the blanket and pillow, as in airlines these days!)
3) The sleeping compartment is a private space: not only do you have a flat bed, but you aren't going to have the person in the next seat slumping over into your space and breathing on you. Lock the door, close the curtains, and it's all your little bailiwick. You can change into comfortable lounging clothes (or PJs) and relax, even if you don't go to bed. There are two basic designs of sleeper car; one has a toilet/sink in every sleeper compartment and the other has multiple toilets elsewhere in the sleeper car.
7) Sleeper cars have a shower/changing room, so you can freshen up before you arrive.
8) Food: Meals in the dining car are free to sleeping car passengers. If you're unwell or cannot get to the dining car for some reason, they will deliver your meal choice to your compartment. Sleeping car passengers can also make use of the "refreshment stand" in each sleeping car, where there's usually coffee, bottled water, and some juices, along with magazines if you didn't bring any. You can of course buy additional snacks in the cafe/lounge car.
9) Sleeper compartments have a power outlet for your computer/cellphone charger/etc. On the trip to LA last spring, I was able to work comfortably in my roomette, with the little table pulled out to support the laptop and its fan-stand. If you're alone in a roomette, you can have both bed and seating available all the time by using the upper bunk for stretching out (it goes up when you don't want it)--this leaves more seat and floor room when you're not sleeping and is actually easier to manage.
Planes are faster for long trips. But depending on how far you live from an airport, and how long you are required to be at the airport prior to boarding, they can be slower for short and intermediate trips. When flying, you're more likely to be bumped because of overbooking, or late because of weather (somewhere in the country, not necessarily near you) that affects your flight, or late (and sitting miserably on the tarmac without access to a toilet or food or even the freedom to get up and stretch) because "there's not a gate available." You'll have to pay extra to check a bag, and current restrictions on carry-on luggage (including those imposed by airlines who have bought aircraft that have zilch room under the seats and very little overhead) ensure that you will have to check a bag if you're a woman traveling overnight on business or someone on a longer trip. If you want a pillow or blanket, you'll have to pay for it; even first-class passengers don't get real food on most flights anymore; the selection of food you can buy on the plane is dismal, etc. You'll be treated like a probable criminal at the airport--tough luck if you have an artificial knee or other prosthesis, happen to have the same name as a "suspected terrorist," or fit the profile usually chosen for the "random" extra check. And the close quarters and recycled air of a plane cabin mean you'll be exposed to more random diseases.
So, until something changes, I'm avoiding planes and traveling by train. I may go somewhere that requires a flight (overseas, for instance) but I'm arranging my schedule for next year around train schedules.