Boiling is the worst way you can do it. Unless you just barely heat the water.
In the process you will liquify the grease/fat, and it will work its way into the bone pores. You will never quite get those skulls as white as you will hope to. And there will always be a slight odor to them.
Neither may bother you, and that is up to you.
the simple rotting in water is the best route if you don't have beetle access.
Though I"ve never tried mealworms, they may be fine.
