If you’re going to work on a particular application of machine learning such as vision or speech recognition, there are a few things to bear in mind. It doesn’t matter too much which application you choose as long as you’re building skills in the underlying machine learning methods. But it’s still worth putting some thought into which application to work on. The ideal is an area where progress is being made but hasn’t levelled off yet. You can find these areas by looking at this article , which has graphs showing the progress of machine learning in many specific applications.