If you ride on the bus, usually you can insist to load and unload the bike yourself. I think that on the train, a baggage handler would take the bike out of your view. As well, you can insist to make sure that the bike is on board your bus if you change busses. Slightly less chance of the bike being damaged or lost.
I think that if the bus fills up too much, they want to leave the largest items behind. There could be a chance that the bike would have to be carried on a later bus, if they have too many suitcases. I think you would know right away if that was happening.
In the past, the train is well-known for being very late at times. The train originates at the other end of the country, and most of the rail line is shared with cargo/freight trains. Any issues that happen on the track tend to create delays, which are additive and even increasing as the train moves east to west.
For example, if the train is an hour late on the first day, it'll lose the scheduled priority time on every section of track following, and it just gets later and later as the passenger train has to be moved to a siding to let the cargo move through, etc. I think I recall trains that were 2-3 DAYS late in arriving. The bus is usually more reliable for being very close to on-time, at least in good weather conditions. The busses run between two cities, so there is less chance of major disruptions.
At least, 10 years ago that was true.
