If you ask me (I maintain a fork of flot on github) there is no reason to use a client-side library for graphing unless the graphs are dynamic. Requesting/rendering/etc tons of images is painful, flot can add and remove data on the fly and re-render -- and that's not even getting into the potential for hovering effects and the like (flash-style).

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).