Just start with any programming language, the most important thing is that you start to code something and get some basic portfolio of actual products. I'm doing Java, which I feel is great for me. It's also the most popular programming language out there atm. Also, you seem to know a lot of languages, but do you know either of them any good? Stick with one main language and then branch out.
There's all kind of circumstances that would affect what language is the best to use, but with your background I would seriously look into maybe designing HTML5 games for starters. And by that same token, I would not recommend learning Flash. Once HTML5 has become fully standardized, you'll see a lot more use of that and Flash may be a poor investment of your time. HTML5 is, as I understand it, built so that people won't need third-parties like Flash to run their stuff. As a result, Flash would become much less relevant.
Based on what you already know, try learning advanced HTML5 and produce some browser games, for starters. Also check out sites like www.photonstorm.com for more information about HTML5 game design.