I work on a data viz product and we've always struggled with a myriad of charting libraries. IMO Chart.js is one of the best tools for charting that has quickly surpassed existing libraries in aesthetics, ease of use, robust community, etc. Big thanks to the Chart.js team for their work!

I wound up building an open-source web service for rendering Chart.js to images for embedding in static contexts without JS support such as email and chat: https://github.com/typpo/quickchart. Maybe some reading this thread will find it useful.