I have used ZingChart in multiple projects. I like it because of its flexibility (especially with its API's) and its ability with large datasets.
To the best of my knowledge the most feature-complete diagramming library available for Javascript/HTML5
FusionCharts is the most comprehensive charting library. It has 95+ chart types and 965 maps
I've used Highcharts and Angular JS in several projects with an awesome results. If you need help with Highcharts, you can contact me at snieto.com
Probably the most built-in features of all the libraries