I'm currently developing an app, targeting both iOS and Android, using Titanium. So far it's going great - I have one codebase with only a few platform specific branches for UI, and completely platform independent business logic.

It's remarkable how little code you have to write to achieve good results with Titanium. Plus, contrary to what article saids, you CAN use external Javascript libraries, but they have to be adopted to CommonJS before usage. There are also many components written by the community.

The downside of Titanium is that they don't cover 100% of APIs that both platforms provide. For example, there is no Radio Button / Radio Group APIs for Android, you have to invent your own solution. I'm sure there are more gaps like this. But even considering this, you'll probably end up having a working prototype much faster using Titanium.

Edit: For anyone more experienced - is there a better Android emulator out there? The stock one is painfully slow, compared to iPhone Simulator.

Edit 2: Developing with Phone Gap seems attractive, but then you dive in and discover that you have to either load up enormous UI library to mimic native behaviour (which always is far from perfect) or reinvent the UI and touch mechanics yourself. Ouch.