Comets and asteroids are both celestial bodies, and they move around the sun. The question as to whether comets are bigger than asteroids might not be accurately answered in that both objects do not exist with equal sizes. Comets exist in different sizes, and the same is applicable to asteroids. This means there are asteroids that are bigger than comets, and there are comets that are bigger than asteroids.
However, if you want a real comparison between the two, then their differences in what they are made of should be considered. For instance, asteroids are small rocky objects, and they are mostly made up of silicate materials and metals, while comets are made up of dust, ice, and some rocky materials. Comets exist in greater quantity compared to asteroids, but asteroids are very close enough to cause great damage to planets like Earth, while comets are not as close to the sun as asteroids because they are very far away from the sun.