I would lean toward Protobuf wherever you can use it. It is designed to deal with issues like this. However, you can't always fulfill some of the requirements f

I would lean toward Protobuf wherever you can use it. It is designed to deal with issues like this. However, you can't always fulfill some of the requirements for it. In those areas, XML strikes a practical balance. Especially if you can use a significant subset of XML. (If you don't need DOM, then use a parser that doesn't produce it, etc.)