Renfe

Pros

• Either meteor or train (Renfe). They both depart frequently from Terminal 4 (arrivals) to the center of Madrid.
• Trains: book Renfe or Iryo now, not at the station - AVE fares climb like airfare.
• Spain's trains are excellent; book on Renfe, Iryo or Ouigo a few weeks ahead
• I could not find a silent car for reservations on Trainline--I did on Renfe--we like it quiet so prefer the silent car.
• Renfe is the Spanish train provider. Looking up train times and buying tickets can be a bit quirky, but stick with it. It is way better than using a third party website.

Cons

• Renfe absolutly does raise prices according to demand
• Renfe can be a bit all over the place with release timing. Some routes show up months in advance, others just a few weeks before. It usually comes down to a mix of pricing strategy, competition, infrastructure works, and the type of train.
• Worth checking both on the Renfe website as it depends on timing.