From what I've observed, Matlab is more popular. There's a perception -- for whatever reason valid or invalid -- that Matlab is for numerical computation, and Mathematica is for symbolic or higher level math. And, that Matlab is easier.

However, I'm noticing a trend towards using mainstream programming languages and whatever free libraries are available, to do the same kind of work. I used Mathematica 15+ years ago, and for doing the same kind of work today, I now use Python and am quite happy with it.