I have been to both cities on my own, specially Madrid, which I love. One thing Ive noticed is that the Regent add on tours in Madrid treat it just as a base to go to places like Toledo and Segovia. Dont get me wrong , those destinations are very special, but Madrid is a fabulous city which deserves several days on its own. Both cities are very different, Madrid is the quintessential Spanish city IMO. I think that to hit the highlights in each city you need at least 3-4 days days in each. Travel between Barcelona and Madrid in train is very easy on the fast train, about 2.5 hours