We've taken the Auto Train four times. Only once have we had a roomette...and I'll never do the Auto Train again without having a roomette.
The roomette is very small, but very private as well. You don't have the contstant noise of people walking down the aisles, kids crying, lights going on and off, and doors opening & closing between compartments. The pull down beds were comfortable, and you don't have to worry about falling out. They're a little slimmer than twin beds.
The seats in coach are nice (in fact, the entire coach section is nice), but trying to sleep on those seats is impossible. Besides the things I mentioned above, the seats don't recline back very far, so you end up in the shape of a potato chip, and for me...that was bad for my back. I'd rather spend the extra money and get a good night's sleep.
The train's movement actually rocked me to sleep, but I've read where it bothers some people.