BEST Format/Protocol for RESTful SOA

Question

Which is the best protocol / format for SOA designs using REST. Here are some options but i can't decide...

• XML
• JSON
• YAML
• ProtoBuf
• ... anything else i might have missed

These are my requirements...

• should be lightweight and less bandwidth guzzler
• should have existing client libs in Python and PHP
• should scale VERY WELL

-- UPDATE --

We have two machines (one is Python -- our middletier) and the other is PHP (front end -- used for rendering different HTML for old browsers, HTML 5 browsers and our Adobe AIR client). We need a communications pipe between the Python and PHP machine -- and we think a RESTful service pipe will be a good idea -- we just can't decide on the format.

Answer 1

Json seems to be growing in popularity and, as a result, has support in various languages, certainly in PHP and Python. And it is certainly light-weight.

I'm not sure how any choice here should not scale.

Answer 2

I personally prefer XML. Its easy to consume and well supported by everything. JSON is lighter and still fairly well supported but to me it being harder to consume isnt worth the saving on traffic. It really depends how much your sending and who is going to consume your api