Security... Monero for example is proof of work. Nav coin is proof of stake.

Over 50% of the monero mining is done by 3 parties. When they turn malicious it has a big negative effect on the security.
PoW relies on miners for security. Over time mining incentive declines due too high difficulty. Small miners have to group up in centralized pools to be able to mine. Bitcoin struggles with this, mining is getting more and more centralised in China.

Nav Coin proof of stake gives everyone the same ability to mine blocks using staking. No big mining rigs needed just coins staking away. It makes it more decentralized and secure long term in my opinion.