Being primarily a mathematician and not a computer scientist or engineer I've used Maple, Mathematica, Matlab, Magma and R. I've also programmed in Python, Perl, C, and Java and dabbled in things like Lisp and Haskell.
All the "math" programs on that list are terrible programming languages; they work great as interactive environments for doing (potentially symbolic) computation, but writing code in them? Ugh. If I actually have to write scientific computing code it's going to be in Python using numpy and sympy, or C if I need performance.
All the different math programs all have their strengths and weaknesses: Matlab kicks the crap out of the other for anything numerical or linear algebra related, both for ease of expression and performance; R has far more capabilities statistically than any of the others -- data frames as a fundamental data type make that clear; Magma is incomparable for the breadth and power of its algebra, none of the other come remotely close; Mathematica and Maple are ... well, sort of a poor jack of all trades that do most things but none of it very well.