For Emily's task of representing how much electricity is used in each of the five streets and showing which streets are responsible for the bulk of the total electricity used, a pie chart would be the best option.
A pie chart visually displays the proportions of a whole, allowing her to easily see how each street's electricity usage contributes to the total. This would help her quickly identify which streets are using the most electricity.
The other options—line graphs, PivotTables, and Sparklines—do not provide the same immediate visual breakdown of parts of a whole as a pie chart does in this context.