Comparison between Corona, Phonegap, Titanium

Answer 1

Here's a more recent and in depth analysis of Appcelerator and PhoneGap: http://savagelook.com/blog/portfolio/a-deeper-look-at-appcelerator-and-phonegap

And here's even more detail on how they differ programmatically: http://savagelook.com/blog/portfolio/phonegap-is-web-based-appcelerator-is-pure-javascript