I think everyone now agrees that in terms of righting moment, the point of attachment doesn't matter. The original question, however, was "which way is 'easier'". I submit that the "easier" way is whichever one requires less pull on the righting line. I'm too lazy to do the math, but my intuition is that a right-angle vector to the body will require the least magnitude pull.

Therefore, you need to determine the height of the sailor righting the boat, the attachment point (harness or arms), the angle that the sailor leans, and the beam of the boat before you can answer the question.

A tall sailor that hauls by hand and leans way back on a narrow cat will prefer a line thrown over the hull. A short sailor who pulls from the waist and stands up straight to right a wide cat will want to attach to the underside of the crossarm.

Regards,
Eric