What I am interested in?
- Presentation model: Can be Flash, HTML Canvas or any other magic. This influences interoperability and scalability of the charts.
- Licensing model: Is it free, commercial or GPL.
- Dependencies: Should I have to bring another dependencies with the chart-drawing facility?
- Docs: quality of documentation.
- Examples: quality of examples.
- And finally, outlook of the charts and number of the options are also matters.
I've found 16 libraries up to now and made an overall matrix about them, regarding considerations above.
Check it out.