I have traveled most of the main AMTRAK routes and rarely bother about taking photos as experience has taught me the results are unlikely to be worth bothering about .... but it is something to do to pass the time and on some of the narrow gauge [Colorado] RRs there may be open cars and 'end platform' to shoot from. But I use trains because I like them not for the photo op.
AMTRAK windows are usually dreadful and if you open a window or door you are likely to be put off the train and the next one is the next day if you are lucky
The most relatively smooth is the Georgetown Loop which has newly laid track post WWII and the worst probably the C&S out of Leadville .... but Narrow Gauge 3ft instead of 4'8.5" Standard is inherently rocky... 2ft Like Cripple Creek even worse .... then I was scared stiff in a near empty winter run train on the UK Dymchurch and Romney Hythe 15 inch railway as the driver in a hurry to get to his tea-break pulled out all stops with Hurricane the loco
Then there is the difference between double deck 'western' Amtrack which just 'float' along swaying from side to side and single deck Eastern which riding over the end bogie was dreadful ... thankfully just from Washington to Charleston ... an overnight but early arrival.