According to Albert Einstein, imagination is more important. However, there is no actual answer to this question. Philosophers have debated it for millennia, and the consensus is that one is not more important than the other. Rather, the two work together to help people form a complete experience of the world.
Einstein's argument for his assertion was that without imagination, he never could have envisioned relativity. Most contemporary scholars, however, argue that it is actually the other way around, though many are hesitant to assign one importance over the other. One modern academic view is that before one can put imagination into context, one must have knowledge. Once knowledge is acquired, it is then possible for humans to use their own experiences to marry their imaginings to what they know.
A recent postulation regarding the importance of imagination is that because contemporary humans place such emphasis on the importance of imagination, they have developed overactive imaginations. This may be a hindrance to properly integrating imagination with knowledge due to a degraded ability to perceive and assess reality.