TensorFlow is better for deployment. Pytorch is better for research. Theano/Keras is simpler to use and a little faster than TensorFlow
"PyTorch is better for research" is a weird, unsubstantiated statement. The fact is that few serious researchers use PyTorch (and even those complain about it). It's mostly grad students in a handful of labs. The only researchers I know who use PyTorch have been from FaceBook, and that's because they were implicitly forced to use it (PyTorch is developed by FaceBook). According to https://medium.com/@karpathy/icml-ac…
My two cents as a researcher who has used theano, caffe, pytorch and TF: they all have their pros and cons. After starting out with theano, I really appreciate the dynamic nature of pytorch: makes debugging and exploration easier compared to the static frameworks. Researchers tend to value these features over deployability, scalability and raw speed (though pytorch is no slouch). So I fully expect pytorch to get a lot of momentum in the near future.