If you have lots of money to burn, a train with the sleeper car or roomette is a better experience. You can at least lay down and have more room to relax, the windows are less grimy, you get better shades, lights, and much more room to lay down and relax.
The whole point of mass transit is it's not a car, so comparing it to driving is apples and oranges.
Greyhound buses run more-or-less on time. The routes are direct, they're predictable, and they will take you where you want to go. They also don't have a dining car, spacious bathrooms, room to walk around and stretch your legs, etc. If somebody has diarrhea, everybody on that bus is going to know it and smell it.
Amtrak is more comfortable in every way. It's also usually late, and subject to delays because of low rail priority. You can't really count on it for anything other than "it'll leave eventually" and "it'll get there eventually". While on the train, it's really quite pleasant - as long as you don't care about arriving when the schedule said you would.
I can easily believe that trains are more spacious and the seating is more insulated from odors.
But my experience riding trains is that they sway/shake obnoxiously while going around curves. Where as busses like Megabus are a very smooth ride the entire way.
> room to walk around and stretch your legs
My experience with busses is that there are somewhat frequent stops where people are encouraged to walk and use the bathroom. Which isn't a complete fix, but it does serve to substantially mitigate those problems.
I've only used one long-distance Amtrak train (as an international tourist), and it was more comfortable than any long-distance bus I've ever used. Loads of legroom, a power socket, a large toilet at the end of the coach, a big window, a decent seat. There's a table if you book it, e.g. for a group of 3 or 4.
My journey was ~12 hours during the daytime. I wouldn't want to sleep overnight in that seat, but it's still going to be better than a bus.
Example with plenty of pictures of inside the train: https://www.seat61.com/california-zephyr.htm and https://www.seat61.com/UnitedStates.htm
I finally got a roomette experience after Amtrak introduced the lottery for lower prices (and to fill empty seats). I really loved the roomette, and the reintroduction of the dining car (I'm old enough to remember when everyone got to dine...). If I had lots of money I would take it all the time.
But most of my experience with Amtrak is coach. On long trips, it's very hard to get comfortable when trying to rest/sleep. Even if you get a window seat (so somebody isn't waking you up to get up), and manage to find a good position to lay in, the whole train is shaking and bumping and banging at odd times, and the cabin is freezing. Add to that the coughing and talking on phones and everything else and it's not a great time. By the time you arrive the next day you feel like you've been in an MMA fight.
The bus is slightly better. It's still not comfortable, but the ride is much smoother, and generally it's a little quieter. You often get a straight shot for 2-5 hours of just steady movement and light rocking, and then a break where you can stretch your legs or use the bathroom (don't ever poop on the bus!). Sometimes they're late, sometimes they're not, and it's always chaos trying to figure out which gate is which route. But in general I don't feel as beaten up and tired after I finish the bus route.
The other reasons to use the bus is it goes where the train doesn't (we have extremely limited rail lines in the US), it's cheaper, and runs more frequently to more places. Buses also take highways where cell signal is available, so if you have a hotspot you have internet; on Amtrak the internet usually doesn't work and on longer trips there's often no cell signal. The bus is definitely a more fraught journey, but the train ride literally makes me feel worse. I guess it depends on the person.
I should add that Amtrak is going to be a much better experience (maybe the only choice, next to a plane) for people with disabilities or the elderly. Long-term parking is also often available at Amtrak facilities, unlike many bus depots. And I will say that the Amtrak quiet car is a thoughtful respite from noise, even if some people don't respect the rules. But I wouldn't travel on any of these lines without ear plugs and an eye mask.
I completely disagree with this. The point of mass transit is to move people from one place to another. I routinely compare driving, trains, planes, buses, and ride shares. They all have pros and cons and it really depends on the trip.