Plugin vs. Widget

Hi,

I want to allow users to put certian js code (for example a stat counter) in their pages.
What I need is:
1. Put a js code in places such as before </body> of between head tags.
2. Allow users to exclude/include pages to the addition(for example a user wants this js code being added only to the “front page” other user wants to exclude the addition from cerian post)

What should I choose? Creating a widget or creating plugin(I have n oexperience in any of them). I guess witget is not good beca use of (2), widget’s “scope” is only inside the sidebar. Is it true?

Thanks.