We don't fly so what is best? Train or bus? Is there high speed travel yet between them? We may consider a stopover to break up the trip. We travel in the spring. Thanks.
As others have lamented, the travel connections between Madrid and Lisbon are surprisingly bad. No fast trains. Long bus or long slow train or quick, inexpensive flight. Flying makes the most sense for many. If you simply can not or will not fly, you can take an (expensive, slow) overnight train or a long bus ride. It's a shame. Maybe someday there will be a good rail option. Right now, not so much.
Correct - there is only one train and it is an overnight. I've taken it and it is fine for an overnight train. But most people don't sleep well or comfy on such trains. And you'll be sharing with others in your couchette. The bus is another option. I believe it is an 8-9 hour trip. You could probably do a stopover with the bus option.