Pylearn2 vs TensorFlow
You might want to take into consideration that Pylearn2 has no more developer, and now points to other Theano-based libraries:


  There are other machine learning frameworks built on top of Theano that could interest you, such as: Blocks, Keras and Lasagne.


As Dawny33 says, TensorFlow is just getting started, but it is interesting to note that the number of questions on TensorFlow (244) on Stack Overflow already surpasses Torch (166) and will probably catch up with Theano (672) in  2016.