To me my investment should fit 2 main criteria:
1: Good potential for future gains
2: A real secure coin for real anonymous daily use. (i'm not a techie and several coins claim to be anonymous, but i'm unable to judge)
1. depends on your time frame
2. Monero is the choice today. Zcash has governance issues (centralisation, premining)
In the future, Bitcoin will almost certainly adopt Confidential Transactions. There's a debate right now about whether to make them mandatory (if they are not mandatory, then it becomes somewhat traceable imo). There's a decent critique of zcash here:
http://weuse.cash/2016/06/09/btc-xmr-zcash/