But, the train isn't always faster, and it can also be more expensive.
So you have to shop around and decide what your priorities are.
The train usually has lots of room.
Bus travel can be good for shorter distances, but I don't think I would do it for long distance unless it's an overnight trip. That way, you can save on accommodation fees. But of course the problem with land transportation overnight is that you don't get to see things along the way! One of the reasons that we would take a bus or train instead of flying is because we want to see the countryside. And taking a night trip means you wouldn't see a thing.
But some of the new buses can be comfortable too.
There's nothing worse than sitting in traffic, and usually you don't have that problem with a train. Bus stations are often situated in inner city neighborhoods and so they have to deal with traffic that can be heavy at times. With a train, you're constantly moving and you pull right into the station without a problem.
Trains often have a snack car and a bar car! If that's not a good enough reason to take the train, I don't know what is. We've often found that it's easier to meet local travelers and chat with them if you can.