If the products you're using are not abrasive, that is if they are not instilling scratches into the paint then theoretically it shouldn't matter which direction you move your hand.
Practically speaking, if the products or process you're using is instilling scratches/swirls, instead of rubbing in straight lines to keep all the scratches in straight lines stop what you're doing an re-evaluate your process, consider changing products or application material until you dial in a system that isn't scratching the paint.
Remember, besides product choice, (type of wax), you also have application material, that is the thing you're using to apply the wax. This needs to be non-abrasive and gentle to the finish also as well as working clean, that is the car must be surgically clean before you apply the wax.
It's easier to spread any product out by hand using overlapping circular motions and an easy thing to prove to yourself. Rubbing a car out in straight lines takes more skill and focus on the task at hand. Usually you would apply product in the direction the wind would flow over the car if you were driving the car or in the direction of the length of the panel if working on thin panels.
Personal preference will always be a factor.
For applying a finishing wax or paint sealant I'll tend to use overlapping circular motions. For working out defects I'll use a combination of both circular motions and straight-line motions.
For applying a cleaner/wax to a neglected finish by hand I would use overlapping circular motions.
Hope that helps...