I'd suggest driving a car. I really doubt the typical person has an Amtrak station closer than the nearest airport.
As far as highways being crowded: This is really only true when you get to the cities. In between cities, traffic generally flows well. The city traffic isn't constant for the full 24 hours. It is often possible to plan your trip so that you don't ever experience traffic when driving.
The exception is the east coast from Richmond VA up to Boston. This section of I 95 is always a mess, and it's not surprising that's the one area of the country where Amtrak does well.
You’ve obviously never been to Texas. I-35 and I-45 between Dallas and points South, like Austin and Houston, are jammed with traffic day and night. ...It’s sometimes faster to travel 250 miles by driving the State Hwys. instead of the Interstates, and more enjoyable as you view the smaller cities/towns and get to stop at local restaurants.