Both cities worth a visit.
In Madrid also you will find a lively City Centre with tipical streets and its artistic and meeting point in the Mayor Square. You can find nice places for a drink and shows. If you are interested in museums you may also visit El Prado or Reina Sofia Museums, and take a rest in El Retiro Park. As well as the Royal Palace and Opera Theatre, with its classic architecture and historic buildings. For further info on Madrid just visit the following link http://www.turismomadrid.es/index_INGL.aspx

Barcelona is a place to walk and discover its magnificent arquitecture mainly inspired by Gaudí. So you can start your way through Paseo de Gracia and see the luxury shops and Gaudí Buildings around, go to the Gothic Quarter to see the beautifull narrow streets that will lead you to remarkable monuments as the Cathedral , the Government Palace or The Picasso Museum. You may also visit Gaudí's Parque Güell in the open air and las Ramblas Market place. You can see all this informationin detail on the following link http://barcelonaturisme.com