I found this on the Wikipedia IOTA article:
IOTA uses Winternitz hash-based cryptography signatures instead of elliptic curve cryptography (ECC).[30][31] Hash-based signatures are much faster than ECC.[32]
Is speed the complete reason, or are their other factors that went into the decision?
One of the reasons is quantum-security.
Traditional cryptocurrencies base their security on elliptic-curve cryptography. Classical examples of such algorithms are the RSA Cryptosystem, Diffie-Hellman Key Exchange or Digital Signature Algorithm, all of which are known to be vulnerable to quantum computers. Winternitz hash-based signatures, on the other hand, are largely resilient to quantum computers.
