I'd go with SVG based on its future prospects for widespread support. Mozilla provides native SVG support; IE 6 requires a free plugin download from Adobe. Microsoft will probably incorporate native SVG at some point (the long-awaited IE7?), unless it makes a conscious decision to try and kill SVG, which I deem unlikely because MS doesn't seem to have a vector-drawing alternative it's pushing.

Mozilla's canvas looks interesting, as it seems to be much like the native drawing capabilities in Windows and the Mac ("canvas" is Apple's term for a drawing surface in the MacOS). Seems to be program-driven as opposed to rendered from an XML document, which suggests that it would be much better at animation than SVG. The problem is that I don't see any incentive for Microsoft to adopt it. From their point of view, you can do all the same things using ActiveX plugins and Windows GDI+ and DirectX, so adopting the Mozilla canvas could undermine their investment in those three technologies and the Windows monopoly itself.

VML? Well, it was a nice try, but never caught on.