We were merely in search of a good web framework. Java has battletested libraries but so does python and a lot of other general programming languages. It still isn't answering our core question.
A decision on what web framework to use has much more to do with the framework itself(its philosophy and community) than with the language it is built in.
Coming to django, I would argue that it is the best documented project on this planet! Django has a huge number of plugins, quickens the process, and is based on some amazing philosophies(DRY) and you happen to admire what a big deal it is when you go deep into design of your web app.
Also, I can even argue that I can get a programmer who doesn't know python to start on Django in 4 hours. Now, I wouldn't bank on this point as it is a language ecosystem point, but it is a true fact, happened to me some years ago.
Lift, is cherry picking features from django/rails, which is actually a good thing, but I see it being a lot less progressive as compared to Django even at the scale at which Django is right now.
Play, I haven't used, so cannot argue much on that. I think Play2 is less than a year old? Surely, I cannot let my startup developers write more bytes than necessary. Why code something which is already done and that is precisely what happened with us when we started working with Django. Well tested libraries can be pip installed.