I'm the main author of Apache Curator (a ZooKeeper JVM client/lib). My biggest concern would be availablity of reliable, well tested implementations. For exampl

I'm the main author of Apache Curator (a ZooKeeper JVM client/lib). My biggest concern would be availablity of reliable, well tested implementations. For example, Curator gives you well tested locks, leaders, registries, etc. If you have to roll your own versions of these things you're bound to mess it up. I've never used etcd so I don't know if it has that. Another thing to consider - is something else in your stack using ZK. ZooKeeper is a component in a lot of existing open source libs: Kafka, Hadoop, etc. So, if it's already in your cluster you might as well use it for other things.