Ether (ETH) has recently been deemed by the SEC as "not a security", and it is necessary to pay for transactions and other resource utilization on the Ethereum blockchain. The main driver of value is the fact that the decentralized applications that will interact with Ethereum's blockchain will be required to pay a "gas" cost (very small denominations of ETH) in order to function.
Currently, this gas cost is distributed to miners, in addition to their reward of newly minted ETH.
Zcash (ZEC) has not received much attention after launch, but was recently added to the Gemini cryptocurrency exchange, and has been rumored to be on its way to Coinbase for some time. It is modeled after Bitcoin (BTC), and unlike ETH which has no apparent supply cap, ZEC has a finite supply of 21,000,000 coins. Currently, transactions are processed in a similar way to Ethereum and Bitcoin, in that miners use specialized hardware to iterate a hashing algorithm, and are given a reward consisting of fees from network users, and newly minted Zcash.
Both development teams have expressed the possibility of moving to a "Proof of Stake" (PoS) system in the future, which would allow for users to stake any amount of currency over the minimum limit. The network would calculate what percent of all staked coins on the network that user owns, and allow them to process an equivalent percentage of transactions, and issue them a reward to the wallet the coins are staked in. That is a simplified version of how it would work, and does not take into account security considerations, and more unnecessary details for the layman.
Currently, the coins are experiencing a bit of volatility, but as the platforms mature, the relative value of their native assets should increase. Ethereum is currently inflating, but the current word is that once PoS is implemented, there would be no further ETH created, and all rewards would come from user fees. It is reasonable to expect that ZEC would not implement PoS until the entire supply was mined, but depending on the foundation's operating costs, it's also possible they could implement this change sooner.
I think that Ethereum has less risk associated with investment, because it has received considerable news attention, and is very developer friendly. Once decentralized applications begin to roll out, a period of rapid growth will begin, and that is where I would plan a momentary sell-off until a reasonable market correction occurs.
As for Zcash, I think that it is a long term buy, and should not be subjected to the same volatility metrics that drive my Ethereum trading. I believe that the limited supply of Zcash, coupled with it's main technology (zkSNARKs) will make it a simple yet essential player in the financial universe of the future.