Personally, I find the ordinary Regional to be substantially more comfortable than a plane, and marginally more comfortable than a car (assuming I'm a passenger - the train automatically wins over driving myself because "spend 8+ hours of my life reading" is immeasurably more appealing than "spend 8+ hours of my life driving".)

The one time I was on a bona fide Acela (it got substituted in for a Regional for some reason), I didn't find it notably more comfy than the regular train, though. *shrug* I hadn't done much train travel at that point, though, so perhaps it was simply lack of comparison data. :)

(Oh - and in money comparisons, don't forget tolls, if any. Some trips, those can be non-trivial.)