What is the best way to implement a diff (file/string comparison) that benefits productivity?
I understand there are many options out there from various desktop applications to enterprise services that examine data on the wire.  What method/means/application for comparison has proven most productive for programmers?

I am hoping for answers that come from personal experience or empirical productivity research.  Please list any applicable tools and how those tools are accessed.  If the most productive diff tool is not your favorite diff tool then indicate your favorite diff tool as well and why it is your favorite.
What is the best way to implement a diff (file/string comparison) that benefits productivity?
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I understand there are many options out there from various desktop applications to enterprise services that examine data on the wire.  What method/means/application for comparison has proven most productive for programmers?

I am hoping for answers that come from personal experience or empirical productivity research.  Please list any applicable tools and how those tools are accessed.  If the most productive diff tool is not your favorite diff tool then indicate your favorite diff tool as well and why it is your favorite.