What tool would you use to modify a sketch in SolidWorks?

The Trim tool is specifically designed to modify sketches within SolidWorks. It allows users to remove unwanted sections of sketch entities, which is often necessary during the design process to refine shapes and achieve the desired geometry. By selecting the Trim tool, you can easily click on segments of lines or curves that you want to eliminate, thereby streamlining your sketch.

In contrast, the Fillet tool is primarily used to create rounded corners between two lines but does not modify the existing sketch layout directly. The Pattern tool is utilized to replicate features or sketch entities in a specific manner but does not change their initial paths. The Section tool is aimed at visualizing and cutting through solid models to examine internal features rather than altering sketches.

Thus, using the Trim tool is the most effective way to directly modify and improve your sketch in SolidWorks.