I think it depends on the scenario.
Methods/functions/classes need a short description of what they do, how they do it, what they take and what they return, if not immediately obvious and that usually (in my code) comes in the form of a javadoc-style comment block.
In-block code, I tend to leave a comment above a block of lines to explain what it does, or one at the end of line if it's a short and cryptic function-call.
