Probably coach, unless sleeping in a seat is impossible/uncomfortable for you.
By the way, for breakfast after you get off at LA, check out Olvera Street (couple places open there around that time) and Philippe's, which has great food and some old railroad pictures & stuff.
We did that trip. We got a roomette. I am glad we did as train back to LA was hours late. And we were really tired. Was nice to get a little rest for LA.