'EQUILATERAL-ness' of Triangles

Here are four measures of 'EQUILATERAL-ness' of triangles. If you drag the vertices of the triangle, the measures of 'EQUILATERAL-ness' are shown in the table on the left. How do you think these measures are calculated? Which of these measures do you prefer? Under what circumstances? What other measures can you think of? When would those measures be better?