Highcharts provides 20 different types of [charts](http://www.highcharts.com/docs/chart-and-series-types/chart-types) to choose from, and they make it simple to [combine](http://www.highcharts.com/docs/chart-and-series-types/combining-chart-types) chart types.
Ranked in these QuestionsQuestion Ranking
Pro Easy to use
Flot provides detailed and well organized documentation that includes plenty of code examples you're free to use. It's fast to customize and add functionality, partially due to its use of jQuery.
Pro Real-time updates
Flot provides live updating with a customizable update time.
Pro Drag to select
Pro Simple configuration
Pro Excellent browser support
Highcharts supports all modern browsers (including IE6 and up), iOS and Android.
Pro Lots of good examples
The site has a selection of good examples that will help you get started quickly.
Pro Library to support Microsoft .NET
Compatable with .NET framework 4+, can develop graphs from server side for ASP .NETand ASP .NET MVC applications.
Pro Good documentation
Very handy with examples and explanations.
Pro Supports multiple Y axes
Important for trend correlation, eg. comparing number of clicks to sale amounts. Not same scales / units.
Con Limited choice of charts
Currently, Flot supports a limited number of chart types (lines, bars, filled area and point chart).
Highcharts is not free for commercial projects, with a starting price of US$590 for Single Developer + Maintenance & Support
Con The examples are not that great
For instance, example's JsFiddle may get stalled when loading.