>>7
Of those alternatives, I'd consider most inferior to XML, as they don't even nest! S-expressions are... okay, I suppose, but they do not clearly separate the tags from the content, and malformed content like mismatched parenthesis can fuck up the parser with no clear indication where the fuckup started.
It's a wash, really, but XML won and is now pretty much the standard.
Being directly executable by JavaScript and Python means shit if you're not programming in either, or if you do not trust the content.