After some research, here are conclusions for the comparison:
PhoneGap and Titanium serve the same purpose: developing cross-platform mobile application.
However, they differ in several aspects:
Many features have been introduced lately (after release of Xcode 4.4) to the syntax of Objective-C. These new features simplify development and relieve the developer from the long code, which, sometimes, can result in unreadable code. In this post we try to give you a concise summary of the new features, as we couldn't find any web page that does.