I feel that copper or hypo are it. Anything else is questionable, at best, and the people that swear that Snake Oil XYZ cured their fish, probably had fish where the Ich dropped off and the fish was stronger in round 2 when it came back and has not shown signs. Fish can have it and not show signs and it can be present in a tank without negative consequences. Fish in a tank with proper nutrition, good water, low stress, etc are perfectly able to keep it at bay.
Garlic entices fish to eat. Fish that eat are stronger than fish that don't eat. Stronger fish have higher immunity to the various nasties. IMO
, garlic helps at times, but can not be considered a cure or even a treatment.