It also depends on what type of damage you want to cause, which will be related to the type of weapon you have.

For example, there isn't much point having a blunt/square tooth on a disc as you won't be fully utilising the inertia and force a disc can deliver. You would want a tapered or pointed tooth to focus that energy into cutting your opponents armour and then any remaining energy is used to toss them into the air/across the arena.

Also, you might want a flat tooth/head on a bar spinner as it has less inertia/force and you want to transfer as much force as possible. Best way to do that is give yourself a larger surface area to increase your chance of a good hit.

However, most people taper or sharpen the teeth on their weapons in some way, even if its just by a few degrees, to get that initial focused force to bite into their armour.

Our robots have two very different weapons. Binky has a 300mm diameter vertical disc with a single tooth, where as Conker 3 has 160mm diameter whisk. They are almost polar opposites in terms of the damage they aim to cause. Binky aims top cut and slice into armour, and use any remaining energy to toss its opponents into the air. Conker 3 on the other hand aims to rip and shock load any joins/welds to remove entire panels of a robot, and again any remaining energy tosses its opponent into the air. Both are very effective, but are quite different approaches.