Drums are probably the most solid and consistent kind of spinner, but carry the least (least huge, it's all relative!) thwack for a given RPM. Vertical bars/discs store and impart massive energy, but can be fragile and cumbersome. Horizontal bars/discs often have the highest energy storage but send themselves flying in a hit, imparting less. It's a much of a muchness really.

In the Robochallenge arena, it seems drums reign supreme. Big vertical discs tend to be sluggish and in the smallish arena that's a problem, whilst horizontals throw themselves out. A drumbot can be quick and nimble. Though for many they don't have the hardcore-factor of a bigole bar which I can totally understand.