Right now Jordi Alba is the clear favorite to start at left-back under Vicente del Bosque.
If the starting role was based on form from the last season-and-a-half, however, the Barcelona full-back would be on the bench for his national team.
The best Spanish left-back from last season and, so far, this season is Malaga's Nacho Monreal.
Jordi Alba is one of the best attacking full-backs in the game and has shown the potential to perhaps become the best at the position one day.
But since the start of last season, Monreal has been a more complete and, quite frankly, better player.
The case for Monreal
The Malaga star is the more reliable player defensively. Last season Alba was consistently suspect at the back for Valencia, and not much has improved since returning to Barcelona.
Monreal gets dispossessed less, he is more calm under pressure, he gets caught out of position far less, he is the better tackler, is better in one-on-one situations and is more useful defending set pieces.
Alba is known for his attacking qualities, but even in that aspect he is not much better than Monreal.
The former La Masia product is not a much better passer at all, he loses the ball more, he is no more successful dribbling past opponents and he takes fewer shots per game.
Why Alba will start anyway
Regardless of the fact that Monreal is the better player, chances are that Alba will continue to start for two big reasons.
First, his performance at the Euros this past summer was just incredible. Looking at the entire tournament, he was Spain's best and most consistent defender and played the best football of his career.
Second—and probably most important—he plays for Barcelona. Some Cules may deny this, but simply wearing Blaugrana has a huge influence on Del Bosque's squad selection.
Monreal is the better player, but Alba has the better pedigree and will likely have slightly better numbers because of who he plays for.
Spain will not suffer with Alba
In the end, while Monreal certainly deserves a chance to play and is the better full-back, Alba is not a great step down and has proven capable of playing at a top level for La Roja.
Also, with the way Spain currently struggle to find goals and break down opponents at times, having Alba's pace and aggressiveness going forward adds a lot to the team.
Monreal also adds a lot in attack and usually with far inferior support than what Alba has at Barcelona, but he may not have a chance to prove his quality before 2014.