There a many reasons, but to name a couple: It has a different approach on blockchain technology, it uses the Tangle which can scale. Transactions with 0 fees > micro transactions. Very high security.

Iota also has a great dev team, one of the best in crypto and with a great trackrecord > Nxt (Pos)

Bitfinex, a massive exchange, adds it, this is a sign imo.

For more info: https://blog.iota.org/iota-development-roadmap-74741f37ed01