[phoboslab]

That really depends on what you want to do. The drawing performance for the canvas element has been dramatically improved in the last few months - for desktop browsers at least.

And then of course, there's WebGL; even if you just use it for 2D stuff (shameless plug: http://www.phoboslab.org/xtype/ ) it's way faster than Flash. I have no doubt that in a few month the the 2D canvas context will have the exact same performance (if not better) as WebGL for 2D stuff.