Madrid and Barcelona are Spain's two most popular destinations. Many who plan to visit one try to fit in a trip to the other. If you're in a similar planning stage, how should you go about doing it?
The first question to ask yourself, as always, is whether you want to organize everything yourself, or if you want to go on a guided tour. The next step is to decide where you'll arrive and if you'll leave from the same place or not.
If organizing everything by yourself, it doesn't matter which city is your arrival point: the high-speed AVE train will shuttle you between the cities in as little as two-and-a-half hours. It's quite expensive, but quicker and a lot more convenient than flying. From Madrid you can also get to Seville by AVE train and then take a train all the way back to Barcelona. Read more here: AVE Trains in Spain.
But if you'd prefer the reduced hassle of a guided tour, then you'll have think a little more carefully about where you're going to start.
Far more tours begin in Madrid than in Barcelona. There is a day trip from Madrid to Barcelona that includes the AVE train tickets and a guided tour of Barcelona when you get there. Obviously, Barcelona deserves a lot longer than a day, but if it's all you've got, then you'll at least get to see its most exciting bits.
There are also some Guided Tours of Spain Departing from Madrid that Visit Barcelona, but again, they only stop for a day or two in in Barcelona.
If you want to spend longer than a day in each city, a tour that begins from Barcelona might actually be your best bet. There may be far fewer such tours, but some of the ones that do exist will start in Barcelona and leave you in Madrid at the end, affording you more time to explore Spain's biggest city. Read more about these tours here: Guided Tours of Spain Departing from Barcelona.
If all that sounds like too much hard work, then you might be better off sticking with just one of the two cities. Which should you choose? This page on Madrid v Barcelona should help you - but whichever you choose, remember to visit the other one next time you travel to Spain!