Let me not get into this fruit-ful discussion (in which I agree with the pineapple - ah well, you know what I mean) and answer to the original post.
I am a (hobbyist) programmer and I know quite some languages. I try to always use the right tool for the job and the same goes here. I must admit however, that -- though I have little experience with MatLab -- Mathematica is a really really powerful package which can do almost anything imaginable. So though probably Matlab is more efficient at some problems (especially numerical ones) I am inclined to favor Mathematica in this dilemma
I have access to a free educational copy of Mathematica, so I use it from time to time to see how efficient it is. But for the problems I do (number theory), I've found that Pari/GP is often 20-50% faster, and hand-coded solutions (when appropriate) are often better yet. So I have little use for Mathematica. On the other hand, for integration there's no equal to be found for Mathematica, so it's all about what you want to do.