We will fly into Lisbon and tour north of Lisbon by bus. Then we need to get to either Madrid or Seville. Should we rent a car in Lisbon and drive to either city and return car to Lisbon or take bus or train to either city and rent a car. I would appreciate your suggestions. thank you
That's pretty far to either of those cities from Lisbon. I would take the train (if not, maybe even check out EasyJet or Vueling for flights).
Unless you are time wealthy, fly - all other forms of transport are time consuming to either destination.
Neil is correct. Flying is cheap and quick. Trains do not work well between Portugal and Spain. Renting a car and dropping off in another country incurs ruinous fees. Take the plane.