I found a very good comparison between Phonegap and Titanium here at the Titanium developer blog.

While the article from an Titanium employee, it's quite objective and as far as I can see, without sales prose.

From my personal experience, I really can recommend Titanium. If you can write JavaScript, you get fast results and you are able to write Apps that use all the native controls of the mobile device. And with Domino To Go, you can replicate and work with Domino data in no time.