Common Lisp is functional in the sense of being based on Lambda calculus, but with all sorts of imperative and OO things bolted on.
Haskell is functional in the sense most people think (maths 'n things, functions with no side effects), with a few 'outs' (monads or 'containers' for doing imperative-like things).
If you want a 'functional' language, choose Haskell. If you want a language you can bend to your will, where you'll be making your own abstractions, writing a DSL, etc..., choose Common Lisp. Actually Haskell isn't even bad for that, so if your friends are using Haskell, just try that.
Haskell is functional in the sense most people think (maths 'n things, functions with no side effects), with a few 'outs' (monads or 'containers' for doing imperative-like things).
If you want a 'functional' language, choose Haskell. If you want a language you can bend to your will, where you'll be making your own abstractions, writing a DSL, etc..., choose Common Lisp. Actually Haskell isn't even bad for that, so if your friends are using Haskell, just try that.