we are coming into Barcelona's Francia station on the sleeper train from Geneva..we need to get to Sants to continue on to Madrid. What is the fastest and most convenient way to do this?
The stations are only three miles apart. I would take a taxi. Here's a link to a map showing Barcelona's train stations. http://www.barcelona-tourist-guide.com/en/maps/barcelona-transport-stations.html
There are frequent suburban trains linking the two which may be faster than the cab for most of the day, given traffic.