Android :: Connect To Google App Engine

I have spent two days trying to decide on a way to upload and download data to the Google App Engine. Do I use REST or simple HTTP post/get? Do I use JSON or XML? Do I use java or Python. I am thinking probably use python and probably use REST. But which one out there? There are so many to choose from. None seem to work out-of-the-box, but need faffing around with bits of code from here and bits of code from there. And is not clear at the outset what am taking on or what the limitations are.