Aleks Jakulin with some nice data on what data visualization works best:
Jeff Heer and Mike Bostock provided Mechanical Turk workers with a problem they had to answer using different types of charts. The lower error the workers got, the better the visualization. Here are some results from their paper Crowdsourcing Graphical Perception: Using Mechanical Turk to Assess Visualization Design:
They also looked at various settings, like density, aspect ratio, spacing, etc.
Visualization has become empirical science, no longer just art.