What is the most useful piece of martial arts training equipment?

There are many useful pieces of martial arts training equipment. But which is the best? Heavy Bags? Speed Bags? Rebreakable Boards? Makiwara? Rubber training knives? Vote on this martial arts poll and see how others have answered this question.

You can find many of these training tools in the wiki's equipment store.

For other martial arts questions & issues, please visit the main Martial Arts Polls section.