(I'm the author) An initial version of SmoothieCharts used SVG, but I switched to Canvas because I got slightly better performance (which actually surprised me

(I'm the author) An initial version of SmoothieCharts used SVG, but I switched to Canvas because I got slightly better performance (which actually surprised me). That's not strictly true - for very large charts, the SVG ones performed better, but I optimized for the common case. Recently I've been experimenting with a WebGL version - it gives MUCH better performance than both Canvas (2D) and SVG, but only works on the most recent browsers.