I have always maintained that if you have an unqualified "favourite" thing, you are probably not very in to that type of thing :)

I use C the most because it is the most appropriate tool for the job at hand for most of the jobs I do. I appreciate the simplicity and elegance of Scheme, and wish I could use it more. I envy Haskell's type system.

None are my favourite. After all, all programming languages suck.