I think the more digital currencies that exist the more opportunities to trade. Ethereum as well as other cryptocurrencies each have their own unique features, but when it comes down to it, it's all about making a profit from them. Yes, I've diversified in eth along with other ones.
Apart from ETH, the Monero and ZCash could be a good choice.
Most good altcoins are rising a lot recently. People start to recognize their values.