Imho the answer is really neither. The leg 'breathes' with the horse, is softly resting over the belly like a wet towel. When the rider then touches with the calf, the horse should move. IF it does not stronger leg merely teaches the horse to ignore the leg until there is more. IF the horse does not move immediately, then it is a whip/bat which backs it up. With a greener horse it can merely be the noise of a bat, the threat of 'ground support' (raising a whip), to a touch of a whip (behind the calf). But whips have an accelerating effect (touch/vibrate quicker or faster/or a twack). Never get lulled into more or stronger, it teaches the opposite of what the rider wants (which is a horse which keeps going unless acted upon).
Or the rider can lift the reins a little (which will cause the horse to CHOOSE forward), or even start to bend the horse. In either case of rein before hand, the leg follows WHEN/after the horse starts to move.
Rhythmic touches are to encourage action of a given hindleg. (ie the belly swings l/r as the legs on one side come together the legs on the other side are apart. By touching with the legs are together, the hindleg on a given side can be encouraged to move more or to push off the ground in a different way.