It really depends on your use case but one of the main "pros" of etcd is the narrow latency band when writing.
This article is likely biased to the good parts of etcd as it's written by coreOS but you can see how the latency of writes in etcd is very consistent compared to the wide range of latencies experienced writing to ZooKeeper or Consul:
There are other "pros" related to the fact that it's been designed for "cloud native" architectures like kubernetes. For example, FoundationDB can perform on average at sub-milisecond latency for writes (https://apple.github.io/foundationdb/benchmarking.html) versus 1.6ms on etcd however configuring FoudationDB to run programmatically is challenging as it was designed in an environment where ops people rack physical servers.
All key/value stores have good points and bad points but that's in relation to your use case. If write or read throughput isn't the most important, say it's consistency or availability, you may make a different choice about what are "pros" and what are "cons".
Another "pro" or "con" may be the language its written in or how it runs or deploys. If you run a Java shop and have tons of experience writing and deploying Java code, it may be in your best interest to be able to have more control by using a project written in Java. conversely, if you have all go engineers, you may want a project written in go. If you only have junior engineers, you may want whatever is easiest to operate and deploy.
