Do those drugs exist? If blackberries, or some extract, work as well as any prospective drugs then I'd go with the berries.
Not yet, but the berries have shown some likely targets for a drug to act specifically upon.
The berries are not very efficacious in stopping cancer, but the genes response they elicit shows us “targets of interest” that may well work wonders when specifically targeted rather than being part of a broad response pattern.
The berries only work (and not berry well) because of specific compounds within them hitting specific molecular targets.