Try them all! And then tell us what you think.

Caffe
CNTK
Deeplearning4j
TensorFlow
Theano
Torch
Many others

About 5+ years ago I was using ML for music transcription problem's, I largely completed my project. I was satisfied I could take any foreign track and generate a visual music sheet so I could play any song I wish. ( I'm rather tone death and not good enough to play by ear, but I'm very good at playing from sheet music.

Five years ago I used MATLAB all can be gotten from torrent, all of matlab has people who provide all the library's for CNN,RNN, and all the Algo's you could want. Almost all the algo's in MATLAB can be read in one page, which makes it easy to understand the algo, and makes it easy to dial-in the fine tuning required for ML.

In the past month I ventured back into ML, as I have a desire to apply ML to code generation and dynamic analysis.

I have spent over a month on all of the 'free stuff' available... Try them all! And then tell us what you think.

Caffe
CNTK
Deeplearning4j
TensorFlow
Theano
Torch
Many others

I have found that for almost all of them you have to spend hours on 'Stack' just to get the installation problems dialed-in, I'm using UBUNTU 16.04, so please ... I have found that NONE of the stuff works out of the box, even the KAPARTHY stuff fails without hours of fine-tuning the library's.

When using MATLAB 5+ years ago I found it to be highly productive, in a few days I was able to choose my ALGO because I could take the dozen most popular models apply them to my data, choose which generated the best results, then I dialed in my +98% and I was good to go.

Now after spending a MONTH on all these Lib's and packages, I still don't even have a single model that can easily migrate to my data.

All is about say tensorflow, but let's be honest its a black box, Theano is great, but its clear they dropped the ball years ago, CAFFE is a pain. The best stuff seems to revolve around PYTHON, which is appropriate for fast modelling, as PYTHON is excellent with abstraction just at the right level for math people.

Most of the stuff coming down from Github appears to be from 2015, the only stuff that appears new is TensorFlow, which of course is GOOGLE which means sure its fun to play and see what their doing, at the end of the day you don't want to be in bed with Google (CIA/NSA)

The rule of thumb is to KEEP-IT-SIMPLE. Keep it Fast, Keep it clear.

Most of the models are all based on the MNIST data, which is ok for a very limited problem set.

IMHO the stuff that's being DUMPED today on the market is a GREAT step backword in productivity. There is NOTHING new that wasn't available in 2012. All that we have now is a dozen different packages that are all hyped by BIG players.

Another item don't even bother to get anything working on windows, as nobody is supporting anything for windows.

CUDA has always worked great with MATLAB even 5+ years ago, all you had to do is "USE CUDA", and your python like MATLAB took care of all the business and off-loaded you work to you GPU, which made the computation 10X. Now the NVIDIA lib's are great, but you have to explicitly use CUDA array's in your code. Even KARPATHY models require filters to go back & forth from GPU/CPU data, as they compress the Pickels/CV differently which is a pain. I would prefer to work in GPU 100%.

Things have NOT gotten more simple. Things have gotten burdensome. Then there are all these languages LUA, JIT, Go, everybody has to start at zero,

PYTHON is now 25 years old and the support for MATH is deep, and PYTHON is almost "APL" like in its power over abstract types. There are people abstracting the GPU but its tough to get the stuff working.

The model seems to be to PUSH people off their private hardware and onto a GOOGLE/AMAZON server for $1/hr to do the training, but anybody that actually has done this stuff knows that it can take weeks of 16+ hour days to find the right training ALGO, then another week to dial it in ( find the right loss-function, and Kernel ), and set the hidden-size,drop-out, and learning-rate, thus in actuality you could eat up 100's of dollars all being FED to google/Amazon.

This is just 'rent' folks instead of OWNING your own computer, you would just become a renter, and of course if your poor then you can't play. I don't like this model.

Even the new laptops have MX980 Nvid Gpu's which are plenty enough.

Tensorflow and its brother's are pretty much designed to be services, which means computation in the cloud.

The real developer thing for the little guy is to get you training model done, and then generate a matrix, and then put it into C, and down load to firmware and now you have an expert system on a $1 CPU, then you can do as you wish, the Amazon model is your trained matrix is held in the CLOUD an everybody uses services from say iPhone/android, ok again its the old nickel paradigm of Oracle, where they tax all transaction by service.

Memory is cheap, simplicity is best.