Use Argon2i when hashing passwords. It provides resistance against side channel attacks with which eavesdroppers could discover the password while it is being hashed.
Use Argon2d when hashing non-secrets, most famously for proof-of-work systems like cryptocurrencies (e.g., Bitcoin) and Hashcash. It provides resistance against ASIC and GPU attacks.
The tricky case is when there are threats of both side-channel and ASIC attacks (arguably any attack against a hashed password). The conservative approach is simply Argon2i with more memory and more rounds. The more risky approach is the less-cryptanalyzed Argon2id.