To expound on the second approach listed, what I've seen is not just a service discovery layer, but client libraries (as opposed to sidecar) that connect to you

To expound on the second approach listed, what I've seen is not just a service discovery layer, but client libraries (as opposed to sidecar) that connect to your service discovery (e.g., Netflix Ribbon which is EOL). Curious what people think of a sidecar approach versus the client library approach? Any preference?