Canvas-based, rendered in IE using ExplorerCanvas that in turns relies on VML
Ico, with an intuitive API based on a single function call to create complex charts
SVG on standard-based browsers, rendered as VML in IE
gRaphael, an extension of the Raphael graphic library
Grafico and Ico are two incompatible forks of the initial Ico by Alex Young. So it is not accurate to state that Ico has become Grafico. Grafico being just one of the forks.
It should be noted that Raphael appears to be no longer maintained. The last commit was July 2010 or so.
Just downloaded raphael charts, liking it lots but no docs, just to forewarn.
SVG is not supported in pre-Honeycomb Android. If being able to view the charts on a broad range of current Android devices is a requirement, you'd have to pick a Canvas-based solution. This article on Sencha Touch Charts goes into more details on mobile charting in general, and why Sencha Touch went the Canvas route.
There are a number of charting libraries based on Raphael, including (but not limited to):
There are pros and cons of both approaches but for a charting library I would recommend the later because it is well integrated with DOM, allowing to manipulate charts elements with the DOM, and most importantly setting DOM events. By contrast Canvas charting libraries must reinvent the DOM wheel to manage events. So unless you intend to build static graphs with no event handling, SVG/VML solutions should be better.