My wife and I (fiftyish) just got back from a 3 week visit to Spain. My first visit in 10 yrs. We drove, flew, and railed between various destinations. Since I used this forum to seek out info prior to my trip, I wanted to report back some experiences.
Barcelona: A great town with a different flavor from any other in Spain. Probably more important and certainly older than Madrid. Depending on your age and tastes take your pick between Ramblas area or Examplie. I chose the latter. Watch out for pick pockets. Even with years of travel experience, I ended up making a donation in Barcelona. Thankfully, everything important was in zippered and/or concealed pockets. Their ruses are very good. Gaudi is great as well as the art museums. Many fine restaurants to choose from.
Granada: A disaster. Has all of Spain's scum ended up in this one town. I loved this town 10 yrs ago and was so disappointed. The Alhambra is now the ONLY reason to visit Granada. Anything else you are interested in doing (including partying) would be done better in one of Spains other fine cities.
Ronda: A lovely town well located for various day trips. It is no more than 1 1/2 hrs driving time from -- Granada, Malaga, Gibralter, Seville, the White Villages, Jerez. Driving is easy in Andulucia except the cities where you should just park it anyway.
Seville: Everyone loves Sevilla. There is a lot to love. The ultimate "just hang out" town. Plus the Alcazar and the Cathedral. The restaurants do not rise above "pretty good" but by this time I was tiring a bit of "typical Spanish food." While always fresh and well prepared, I find it a bit bland after a while and wish they would import some of Mexico's spices and flavorings (or Italy's, or France's or Blegium's, etc.)
Madrid: This city has really improved over the past ten years. More international in every way. Great fun, easy to get around, many eating options. The Prado and the relatively new Museo Reina Sofia are terrific. See a bullfight if you can. More a spectacle than a sport, it is culturally important. But gruesome. It took me a while to sort out my emotional responses to the event. There are two classic daytrips (via train) Toledo and El Escorial. Both worthwhile if you have the time.
Every traveler needs to vist Spain for it art, history and culture.