Earos: On the Brink
Tieflings appear so seldom, and have no apparent cities or settlements that it is impossible to say for sure what classes they might trend towards. Most view the Tieflings as dark servants of evil Lords or Gods and run them out of their lands.
Tieflings are extremely rare and seem to have no lands of their own. They appear at random when they choose, and seem to always have some type of plot or evil intent.