Ask HN: which platform/framework should I begin game development on?

I have been a programmer for well over a decade, and have been working at a big company for the past 4 years, and am familiar with Java, C#, Javascript, HTML.

I would like to develop something on my own in my free time and I have a few ideas for some games that I would personally find fun to play. These games are 2D and can be extended to support multiplayer.

I have no piror game development experience, other than some copying BASIC code from some magazine in the early years.

For a start, I just want to have something working. Thinking ahead, it would be nice to have some revenue, and even have the games on multiple platforms without having to rewrite everything.

Should I use Java, Flash, HTML5, Javascript, iOS, XNA or some other game development frameworks or engines?