I use Python a bunch and have used R in the past. I've dabbled in Julia and both APL & J. I know just enough to say that APL & J are much more expressive as long as Python doesn't have a fix_problem() method built-in. I believe ScottLocklin says something similar below, but he has a lot more experience in R and J than I.

Now q/kdb+ might be expensive, but I can only dream of doing analysis using it. SQL is great, but having the full power of K And Q-SQL would be pretty awesome.