Personally, I'm a big fan of YAML, it is expressive, easy to parse, read and write, but none of that is relevant for your question. Just use the format your co-workers are most familiar with, or even use all of these formats. It wouldn't be to difficult to write a routine that can translate each format into your internal data-representation and back again into another format.

The only formats I wouldn't use are those that are directly evaled as this will have important security concerns or those that put the data into modules, again for security reasons.