Test the well first. Oxidation plus filtration is often the best whole-house path for meaningful iron, while a softener can sometimes handle modest dissolved iron when hardness treatment is also needed.
Best for significant dissolved iron: oxidation + media filtration
Air-injection or other oxidation systems convert dissolved iron into particles that filter media can capture. RKIN and SpringWell both sell whole-house systems in this category.
Best for iron plus hardness: combined treatment train
A softener may handle some dissolved iron, but high iron can foul resin. For many wells, dedicated iron treatment followed by softening is more robust.
Visible rust particles need sediment control too
If iron is already oxidized and particulate, upstream sediment filtration may be part of the solution.
Test before buying
Iron concentration, pH, manganese, sulfur and hardness all change treatment design. A lab or well-water panel is more useful than buying from stain color alone.