All of these frameworks are "relatively new". TensorFlow: 1.6 years. CNTK: 1 year. PyTorch: 0.5 year. Are they really impossible to compare?

> When people say PyTorch is better for research, they mean

That's not what "people" say. They tend to say the opposite. Maybe we can ask OP what he meant when he said it.

> it is easier to implement non-trivial network architectures with it, such as recursive network

It is interesting that you mention recursive networks. There are only a few dozens of researchers who work with recursive networks, and they are all accounted for, we know what tools they use. They use Chainer and DyNet.