Lisbon to Madrid - Fly or Train?

You'll have to price it out. Such flights are often quite economical, but they can vary. I've taken the overnight train and it's fine for what it is. But if you've never done one before, it is not very restful and the trains leave rather late in the evening. I always find it challenging to find something to do until 10:00 or later.

I looked into the same thing a couple of years ago but from Madrid to Lisbon for my group of three. We ended up flying with Vueling and all three airline tickets were about the same price as one overnight train ticket.