NEM is faster, safer and easier to use but Ethereum has a broader way to create custom decentralized apps.
A major difference is that Ethereum put its code called "smart contracts" on to the blockchain and NEM uses code off the "blockchain."
Code on the blockchain is hard to fix if there is a bug or an exploit, so writing data management apps can be a hard process in Ethereum. There is a lot of risk involved, NEM has a solution for this problem, NEM would only put data and assets on the blockchain, making it lighter and faster. NEM comes with a bunch of data management apps built right into the client. These are called smart assets!
Smart assets allow you to create data records and tokens and crypto's and voting systems with only a few clicks!