How to decide whether to use AIR or Titanium
Although AIR is not yet open source, its stack technology (Flex, Webkit, etc.) is open source. Titanium definitely looks promising, but has no place near the moment and support for AIR is not yet available. Until it was released and had a few production apps on it, I wouldn't bother putting too much on it. If you want to participate in an open source project and actually work and help it, something else ...
To clarify, AIR allows you to use HTML / js to build your applications.
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Just in case someone comes back for this post, I'll add 2 cents.
The Titan has appeared in the last few months. It now supports Ruby and Python. You can code your own C ++ modules (like IRC) and compile Titanium to support that module (or you can code modules in Py / Ru / JS).
You can use flex, flash and silverlight in Titanium. All have been tested and work flawlessly :)
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Neither, as both technologies are designed to build desktop applications, not RIAs.
Now if you were asking how you should create your RIA ... so if if you get a desktop version what technology should you use Flex or Javascript / HTML?
The answer becomes obvious if you decide between Flex or Javascript / HTML. If you are running Flex, your desktop application will be in AIR; If you are doing Javascript / HTML your Descktop app will be in titanium.
My suggestion, go with Flex - Air. Both are environments in which the state is simplified. Flex are written as client (desktop) applications anyway because they have state.
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