Going TO the airport I always get off at Sants and take a cab - usually about 22 euros (m o m) Coming the other way from the airport take a cab to Francia where the trains originate (same cab fare as they go a faster route).  If you've got the times right (and a timetable) you can get onto an empty train at Francia and watch the crowds fight for a seat at your leisure.   The Park Hotel opposite Francia is a goodie if you have an early or late flight (room rate about 70 to 80), cabs from Francia opposite.