Ask HN: Best field for a computer engineering PhD?

I am about to begin my active search for a PhD in computer engineering. However before going further, I want to know what is be the best field to attain expertise in (according to HN); i.e. what type of knowledge is the most valuable?

The field of machine learning and data mining is the one that seems to offer the most opportunities today, with the continuing growth of the internet and the ever increasing amount of data available. I would like to study evolutionary and genetic algorithms - is there interest for these techniques as well?