I have seen a wide variety of techniques employed for the human flag/side lever. For example, Dominic Lacasse's flag has incredible vertical symmetry. Both his arms are straight, and there is very little twist in his torso. If you were to rotate a picture of his flag 90 degrees, it would appear as though he was standing on the ground, extending both arms overhead in a Y shape. The french hand balancer Willy Weldens also has a very symmetrical flag that he can hold for over 40 seconds. Al Kavadlo, who also has an impressive flag, sometimes performs a flag in which his body is slightly above horizontal, and sometimes has more rotation in his torso. Among all the people I have seen execute this skill, some have more torso rotation, some bend the top arm or have the arms at different angles to the body, and some have the body slightly above parallel to the ground.
My question is what you would consider a more technically correct flag, which style is more difficult, and what differences are there in muscle activation between the styles? Personally I prefer the more aesthetic and symmetrical style of Dominic or Willy, but as I cannot perform the flag, I am curious about the differences in difficulty and muscle activation.