Flash is proprietary, expensive, and supposed to slowly be going the way of the dodo - particularly as HTML5 gains popularity. Already Flash is unsupported on new Android devices (which might be a good target platform for such an app). On the other hand, Python is free software, cross-platform, and is only getting bigger.
PyGame support for Android is increasing (albeit slowly) with projects like this. Some indie game developers such as the developers for the Binding of Isaac seem to be in the process of rewriting their games to move away from Flash to avoid bugs and improve cross-platform compatibility.
If you're interested in releasing your game as free software and potentially getting other people on board to improve it, I expect Python will give you a much better chance of being successful in doing so. You may even be able to get your game packaged in the official Debian main (or Ubuntu universe) repositories if it's interesting enough - but that won't happen with Flash.
To answer your question, either language will do the job. If the above points are not a concern and you just intend to work on a small hobby project where your primary focus is to just get it done, the language of choice should probably just boil down to your own preference.
I would rule out flash for the same reason as boltonics and bring in Java and any of the c languages as other possibilities. If you have any PHP experience, I think you might have the most fun with python (pygame, panda3d, etc)
I do not want to create big complicated game just simple 2d rpgs or side scrollers etc etc
Ya I thought about bringing that up, but that also tends to stop one from diving in and learning.
What Boudre0aux is trying to say, without saying anything, is that a "simple rpg or side scroller" is actually pretty complex, or can be. The most common intro game would probably be something like snake or pong, but the reason I did not say anything is because this is how one learns.
One has to take up a project that is over his head and has to have a great passion for it. So go for it if you won't have the passion for a pong like game, whats the point otherwise right?