Honorable mention goes to battle ropes; my runner ups are dumbbells, kettlebells, and suspension trainers such as the TRX. They are all awesome tools but they are runner ups for a reason.
The overall, hands down winner: Sandbags!
I have virtually unlimited exercises and movement patterns to complete. I have more options, especially for combination exercises and compound movements, more than any other fitness tool and I say this after using dumbbells “since the beginning of time” and putting equal time and effort training with kettlebells, TRX and Sandbags.
The other training tools work well and can act as a stand alone fitness tool for training the general population; but for certain groups they fall short.
Sandbags can be a stand alone fitness tool, for everyone, regardless of their goal in mind – athletes, bodybuilders, and weekend warriors. They offer better FUNCTIONAL load progression than traditional free weights, better ABSOLUTE load progression compared to suspension trainers.
I can take them anywhere, and USE them anywhere. I have water fillers I can fill at home, or take empty to any destination and fill there: on a plane trip, in a backpack up to a lake in the mountain, or to the beach and need nothing but open space and filler, which doesn’t have to be limited to sand.