Yeah, I don't see it. I looked at a few cases where there's close overlap in the work and mostly what I see is that the ITU doesn't want me looking at the draft stages of documents, which I guess isn't crucial for your implementation work. I couldn't see any particular higher quality though I suppose if you like PDFs and hate text that might go in the ITU's favour.
The ITU has a slight edge in that their published standards are generally of a higher quality and easier to implement.
I care about utility not about nominal designations.