I don't know what to pick, but something else than PDF for the task of transferring documents between multiple systems. And yes, I know, PDF has it's strengths and there's a reason why it's so widely used, but it doesn't mean I have to like it.
Additionally all proprietary formats, specially ones who have gained enough users so that they're treated like a standard or requirement if you want to work with X.
When PDF was introduced it made these things so much better than they were before that I'll probably remain grateful for PDF forever and always forgive it all its flaws.