The most effective chart for encouraging the audience to focus on the differences between various groups in the data would be a bar chart or a column chart. Both of these types of charts visually represent the comparative sizes or values of different groups, making it easy for viewers to quickly discern differences between them.
If you have to choose one, the bar chart is often preferred for its clarity, especially when comparing categories with longer names or when there are many categories. However, a column chart can also be effective for showing differences, especially when the categories are fewer and the orientation works well for the data being presented.
So, either a bar chart or a column chart would be ideal, but the bar chart is frequently emphasized for clarity in comparisons.