Xamarin vs Phone Gap
Kevin Ford, Ken Ross, and I built an application twice (source code available at GitHub.com/Magenic/WhitepaperPerformance) once in Xamarin and once in PhoneGap. The white paper discusses the pros and cons of each platform as well as the performance metrics we saw from each when hitting the same Azure back end.
The white paper is available here: http://magenic.com/xamvphg