>circle wins, obviously.
It isnt that obvious.
>1. more efficient. you can get more area out of less material
So what? It is supposed to be a fight, not an economic way to get more from less. This is not tailoring. This is a fight till death. Less is more does not apply here.
The circle does have more area than the triangle in this fight, but in no way does that change the outcome. The moment the circle gets punctured it has become just a line.
>2. sturdier. it takes significantly more force to crush a cylinder than a triangular prism because flat edges are more prone to bending.
Again: So what? Like I said before, the angles of the triangle can act as razorsharp knives, especially the angle of A is to be feared. In an attack the triangle could make a slide towards the circle and jump at the last moment.
The circle can only roll over his opponent. The circle is simply to big to be able to crush any line beside A-C. The circle would get stuck in the other cases. As said, to be able to cause damage, it then should attack from below, which could crush A-C. But this is unfair fighting.
Unless Circle has hidden powers to become a singularity thus completely able to obliterate adversary, Triangle wins.