Although I love Flash, I decided to dabble in HTML5 to see how easy or difficult it is to produce games in it.
The end product of the tutorial is a simple playable game. However, you have to jump through a lot of hoops to get there. This means that HTML5 for this kind of game is fine for the end user, but harsh on the programmer.
It also seems that HTML5 could be applied to simple games, like this one, but it would be a real pain to program a more advanced game in it. This is where Flash shines.
Flash, of course, is not available in-browser on the iPad, whereas HTML5 is. Android supports HTML5 too.
So I'm going to experiment and convert Drench (flashbynight.com/drench) to an HTML5 game and see how it goes.
I don't like HTML5 at the moment, and I'm experimenting with it grudgingly... but people say it will improve over time.