It's no contest: you want to learn Python.<p>Other commenters (or their links) haven't mentioned Theano, which is excellent for deep learning, so I'll contribute that to the discussion.
I would say Python.<p>I am no expert in neither Python nor JS. But, the AI community really seems to be obsessed with Python and moreover many specific libraries [1] are available in Python that concentrates on AI alone.<p>On the contrary, AI in JS is mainly being used in games and like.<p>[1] - <a href="https://wiki.python.org/moin/PythonForArtificialIntelligence" rel="nofollow">https://wiki.python.org/moin/PythonForArtificialIntelligence</a>
This shouldn't even be a question. Python has, just off the top of my head:<p>1. Numpy<p>2. Scipy<p>3. Pandas<p>4. Orange<p>5. Gensim<p>6. Scikit-Learn<p>7. NLTK<p>What does JavaScript have that even comes close?