We will be renting a car to drive to Laguardia. Is there an advantage to renting a car at either the airport or Sants train station?
An airport will generally have a greater selection, but overall, there probably isn’t much of a difference as long as you’re headed out of the city. Out of curiosity, where/what do you plan on visiting on the way to Laguardia?
If you must have an automatic, the airport is probably better. Otherwise, the train station is easier to get to - short taxi ride from the historic center - and it's not hard to get out of the city. Best to have GPS in any case.