(personal opinion, not speaking on behalf of my employer)

Start out with protobufs, so you can take advantage of gRPC[1] and all of its libraries and all the other tooling that is out there.

If you profile and determine that serialization/deserialization is actually a bottleneck in your system in a way that is product-relevant or has non-trivial resource costs, then you can look at migrating to FlatBuffers, which can still use gRPC[2].

[1] https://grpc.io/ [2] https://grpc.io/blog/flatbuffers

Ah, good tip, thanks!

I'd agree on starting with protobufs, precisely because it's the go-to. Other options have plenty of advantages, but none are as widely supported.