Pardon me for not noticing this earlier. Chris Black from BlackCJ.com has performed a very interesting analysis of content rendering as well as battery performance of Adobe Flash and HTML 5 multimedia that shows that the former is actually pretty good when compared to HTML5. According to him, Adobe Flash on a Nexus One renders at 57 frames-per-second that is significantly higher than the 40FPS that HTML 5 was rendered in on the same device. He also points out that the battery consumption while accessing HTML5 was double the battery consumed while rendering Flash.
Check out these video and images from the study that make up for a pretty interesting analysis.
Battery consumption after 10 mins (in % of battery life)
You can test the frames-per-second of both these formats on your own Android phone (or only HTML5 in case of the iPhone) by checking these following links from your mobile phone