None. Plain ol water and good diet combined with proper trimming.
Dry feet are good. If its really exceptionally dry as a drought and the hoof can't be properly trimmed and is holding false sole because of it, I give the horse a good bath and let him stand in the shade in his puddle to dry. When he's about dry but his fetlocks are still wet, the hoof will be damp enough to trim.
Hoof conditioners do at best nothing and at worst actually harm the horn. The Horse | Hoof Dressings: What Studies Show | TheHorse.com