You can consider Ethereum for your portfolio as the coin is the best choice for a long term investment right now.
Ethereum has one of the best blockchains and has a market capital of $21.4 billion right now and since its origin in 2015, has shown a 1100% increase in its market capital and is growing ever since. Ethereum has a very good development team behind it responsible for its successful projects. The coin has the potential to cross the $700 mark by the end of 2018 and you can expect good returns from it.