To answer your question (without ecuations) Miguel first we must talk about type of loads and loads directions. Section A can be stiffer than section B in torsion while section B can be stiffer than A in flexion. Also, an oval or elliptical tube is stiffer if bended (flexion) in one direction (longer axe) than in the other (shorter axe), passing through all intermadiate states from the maximum to the minimum. A circular tube has the same resistence to flexion in any direction (revolution simetry).
The key to visualize and understand how flexion works: you must learn how to calculate (at least intuitively
) second moments of innertia (dunno if called like this in english) regarding axes (X or Y for a given section). But unfortunately you asked for no equations... 
The key to visualize and understand how torsion works (for closed sections): membrane theory! Just imagine you are holding the tube in your hand and you cover the hole in one extre with soap, while insuflate air from the other side. The soap will "inflate" forming a bubble (a membrane). Try to picture in your mind that membrane. In the places where that inflated membrane has the maximum slope, there you will have the maximum torsion tangencial tensions. A section wich is stiffer on torsion is a section where a membrane would not "inflate" so much.
Opened profiles (C, L, I) are not good for torsion. "I" profiles are the best for flexion.
