but I wonder whether Amtrak has the similar quality as the dog.
If the question is comparing greyhound to an Amtrak train, then the train is MUCH more comfortable and spacious than the bus. If the question is whether the Amtrak bus is better than the greyhound bus, it probably varies depending on bus route and who operates the bus. I would ex[pect them to be roughly comparable. I have only been "bustituted" once, for about a half hour's duration, and it was a very modern, up-to-date "motorcoach", comfortable and quiet, but it was very late at night (actually about 2 am) and everybody was pretty tired anyway.
Calling the USA Railpass a "pass" is actually misleading, I think. It's not a "pass" in the sense that you can just show up at the rail station and get on a train. YOU CANNOT. It is a "pass" only in the sense that whatever coach seats you book for the duration of the pass are considered already paid for. After you buy the pass you MUST reserve seats on the individual trains that you intend to travel on. Otherwise you cannot travel. The pass by itself is worthless without a booked reservation on the particular train. This is where we find the problem.
Let's say for discussion purposes that there are 320 seats in the coaches on a particular train. I don't know just how many seats on a particular train are allowed to be sold at the lowest price before the price goes up. For purposes of this discussion, let's assume that Amtrak may only allow 25 seats to be sold at the lowest "bucket" price level. When those 25 seats have been sold, the next 50 seats will sell at a higher price, and then the next 50 at a higher price still, etc. A railpass seat MUST be a "lowest bucket" price seat. So after 25 of the 320 seats on that train have been booked by other travelers, a railpass holder CANNOT reserve a seat on that train with his railpass, even though there may be 295 unsold seats, because those 295 unsold seats are now selling for more than the lowest price. Personally I think that is a ridiculous policy by Amtrak, but I don't run the company.
If you are planning to travel during a time when most or all of a given train's coach seats are usually sold, (around any popular travel holiday, especially) it is absolutely mandatory that you as a railpass traveler buy the "pass" AND reserve your seats, on all those trains, very, very early. Many months in advance, in fact, so that you will have the best possible chance of actually being able to reserve the seats that you need, with your pass. And even then, you may have to move your travel days up or back by a few days on each train in order to find a day that still has railpass seats available. That, in turn, means you may be spending more or less time at each intermediate destination than you had planned to, or you may have to actually pay extra, to reserve a higher-priced seat on one or more trains during your journey, because railpass seats were not available on those trains for those dates, in order to actually complete your planned journey.
I hope this helps make more sense out of the railpass situation. The railpass isn't really a "pass" - the way Amtrak is currently administering it, it's more of a "hunting license" for cheap coach seats, not a "pass". And I think they need to re-think what they are doing with it, to, at the very least, include a policy that says that if a railpass holder has successfully managed to reserve most, but not all, of his planned itinerary, with eligible seats, Amtrak will allow that "lowest bucket" rule to be bent sufficiently for that pass holder so as to avoid gaps in his or her travel.