I think using Google Chart API is much better than using these plugins. Lots of chart types, easy to make, gives high-quality result, and support all browsers that can display images.
Flot also supports all reasonable browsers (including some unreasonable ones, like IE6). If you find a bug in either the 'official' flot or my fork (or any of the forks of my fork :)) then you should be able to report it and have it fixed quickly enough (or, fix it yourself, the code isn't especially complicated).
Flot, and all other Canvas-based JS charting solutions, are really impressive applications of Canvas, but until browsers start supporting Canvas copy/paste better I'm hesitant to use them for graphing apps. Image-rendering graphing solutions support most browsers and can be easily copy/pasted into other applications, with little additional overhead.