Wwweeellllll,
That depends on a number of things…
Riding a bike is definitely out of the question and there is no way I am going to sit that long on a bus. I’ll ride for a couple of hours if I have to but not for that long. I’ve travelled on a bus for five or six hours and that was more than enough.
I don’t drive, so if it’s in a car, somebody else will have to drive.
I love riding the train but going across country would take a few days, so if I wasn’t in a hurry, the train would be the way to go. I really enjoy riding on Amtrak. There’s a chance to look at the scenery, there is a place to buy food, a toilet larger than a phone booth, and plenty of time to sit and work and read.
But if time is a factor, then it would have to be a plane. A few years ago I made a cross-country trip for my Dad’s birthday. I ended up flying, but I really wish I had had the time to take the train. It would have been great to see the landscape.
As a photographer, getting the chance to film some of our nation would have been really great!
The big problem with traveling 3,000 miles across the country would be that I don’t do well when it comes to sleeping when I travel and it takes a few days to get from the east coast to the west.

Thanks for sharing, I chose a bike as well!