Gyro will give you fast response and is unaffected by actual acceleration, but will drift with time and does not provide absolute orientation. You need both a gyro for fast response and an accelerometer to correct for drift.
In some circumstances just an accelerometer will do, but they can pick up a lot of noise (vibration and accelerations) not just tilt. For an accelerometer to measure changing tilt best it needs to be on the axis of rotation (which for a bike is at ground height unfortunately). Gyros measure angle exclusively and aren't critical in placement.