Best UDF serialization methods?

[th0ger]

Numaflow uses GRPC/Protobuf serialization at the core platform level.

But I wonder, what's the community's most popular serialization method for UDF at Datum level between two numaflow vertices?
(I.e. (de)serialization of Datum.value.)
JSON? Avro? Proto? MsgPack?

[KeranYang]

I have noticed that many teams primarily use JSON. However, users technically have the freedom to select the SerDe of their preference.

[vigith]

There are users who send even pickle'd data between the vertices (mostly ML use cases).