As a .net developer, I would prefer to go for Mono Android. I personally have been developing Android Application for the last few years both in Java/Davlink and Mono C#.
Like java, Mono C# Android is capable of creating powerful Application.
Even in few cases, I find working with Mono C# more comfortable than Java when comes to communicate with Webservice and WCF.
Moreover, there is a learning curve, if you go for java as you have already a knowledge in .Net.
One thing to note before you start developing Android Apps in Mono -
There is a licence fee to deploy apk file in device (USD 399). It is free to develop application and test in emulator.
Apart from this, Xamarin Mono C# is awesome and you can even use your existing business layer and data layer with minimal change.
Check my latest article on Android Mono C#
Android - Stock Market Watch (COINS) in C# using Visual Studio 2010