Depends on what? The complexity of the model, its purpose and the technical ability of the administrator left to maintain it after the implementation and their level of comfort with TI vs rules.
I would also say the field should be expanded to include manual entry. In most cases it's going to be a mixture of all 3.
If I have to pick a side I would say rules as this is a more "elegant" approach vs. the "brute force" of TI.