I hesitated to say that, but to me the most important part is paradigm and structures/patterns. lisp will teach you untyped tree recursion and metalevel perspective. ml/haskell will teach you typed composition. prolog goal based space exploration. forth stacks. APL arrays. C/Pascal etc are supposed to teach you 'imperative' but I believe imperative is mostly a conflation of lots of things, mutable state.. at best you'll learn state machines.