Since angles BAE and FAC are straight angles, this means that they each measure 180 degrees. The angles BAC and DAC are formed by the lines and ray intersecting at point A, making them adjacent to each other and on the same straight line.
Therefore, the best angle relationship that describes angles BAC and DAC is supplementary angles, as they add up to 180 degrees (i.e., the measure of angle BAE or FAC).
So, the correct answer is: Supplementary angles.