Botox injection will weaken and thin the masseter muscle over time. Drilling the bone actually reduces the size of the angle of the mandible (jaw bone) and leads to some scar tissue of the area.
Botox results will be more modest but has much less downtime. It will take months though to see the results.
The surgery is more direct and thus the results will be greater after swelling and edema resolves.
Hope this helps.
Best of luck,