Well, normally in neutral matches where I don't have a preference, I employ the "Where were you in WWII?" corollary.
For example, yesterday I was nearly alone in cheering for Russia. When asked why I was rooting for the Commies, I replied, "where were they in WWII?"
Now I'm not saying the Soviet's were saints, especially in the Baltics up through 1942, but even Hitler didn't think enough of them and their allegiance and by the time the Germans invaded Russia, the Soviet's were firmly in the Allies camp. Couldn't say the same for Spain.
Now, when it comes to two Axis powers, I usually root for broken legs (I even vowed to boycott a Germany/Italy final). Spain, being the weakest of the Axis powers, and driven more by Franco than the Spanish people at the time, get a small reprieve.
Therefore, I'm pulling for Spain tomorrow, somewhat begrudgingly.
That being said, I think the krauts win 3-2.