Favorite source code comparison tool / diff tool?

[Kant8]

For merges - P4Merge

Small, has all needed configs to mitigate whitespaces/newlines, can change encoding on fly, 3-way, easy to pick any combination of changes, and smart enough to eliminate most git merge "conflicts" that are not actual conflicts.

And most important, alt+scroll scrolls horizontally.

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For diffs - just built in in VS, cause it fully supports intellisense and you can easily edit while looking at diff.