I recommend using SVG across all browsers and mobiles. Primary because SVG is working very well on iPhone/iPod Touch, sometimes magnitude faster than Canvas. SVG is using vector graphics (retained mode), which seems to give some performance boost, unless raster (bitmap) graphics is what you need.
I can't recommend any library since I'm coding SVG directly. Raphaël (http://raphaeljs.com/) library seems to be popular, however don't forget Ample SDK (http://www.amplesdk.com/examples/markup/svg/) which can be used beyond graphic borders (SMIL).
For best results, use the Firefox browser..