This thread is perhaps very very old now. But want to share these results for someone who see this thread. Ran a comparison betn. Flotr2, ChartJS, highcharts asynchronously. Flotr2 seems to be the quickest. Tested this by passing a new data point every 50ms upto 1000 data points totally. Flotr2 was the quickest for me though it appears to be redrawing charts regularly.
http://jsperf.com/async-charts-test/2
