When comparing Xamarin.Android vs NetBeans IDE, the Slant community recommends NetBeans IDE for most people. In the question“What are the best IDEs for Android development?” NetBeans IDE is ranked 3rd while Xamarin.Android is ranked 5th. The most important reason people chose NetBeans IDE is:
NetBeans is a free, GPL-licensed IDE. It can run on any computer with a Java virtual machine. If a computer has a Java virtual machine (JVM), Netbeans can run on it. Netbeans can, therefore, run on a variety of operating systems such as Windows, *nix, and Mac OS.
Specs
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Pros

Pro Cross-platform
Xamarin is a platform on which you can build cross-platform mobile applications for Android, iOS and Windows Mobile and use only one codebase.
Pro Fast build
Faster compared to Gradle-based systems.
Pro Allows .NET programmers to write Android Apps
Allows .NET programmers to write Android Apps.
Pro Programming in C#
Allows you to write your programs in C#, a language much superior to Java, regarding expressiveness, readability and overall productivity.
Pro Open source
Xamarin.Android and the whole Xamarin SDK is free and open source and released under the MIT license.
Pro Cross-platform
NetBeans is a free, GPL-licensed IDE. It can run on any computer with a Java virtual machine. If a computer has a Java virtual machine (JVM), Netbeans can run on it. Netbeans can, therefore, run on a variety of operating systems such as Windows, *nix, and Mac OS.
Pro Good refactoring
Pro Easy to learn
Very easy to learn, unlike e.g. Eclipse (which is probably the most flexible).
Pro Good support for integrated Database e Servers (E.g. Tomcat)
Pro Multiple revision control system integration
Pro Customizable theme
Pro Take less memory
Cons
Con Lacking third-party library support
Having to use third-party libraries in Xamarin can be a real pain. Since Xamarin uses C# and third-party libraries are written in Java, you have to create bindings to use them in a Xamarin app. Which is cumbersome and wastes a lot of time. Especially considering that the Xamarin docs are not very good when it comes to this part.
Con Too large to download
Since core Visual Studio comes about in 543 MB of download size, the Mobile App Development with C++ workload comes about ~4 GB, the issues with your bandwidth and internet connection can cause the components to re-download, wasting a considerable amount of internet.
Con Little support for UML
Unless you load extensions.
Con Slow
The Netbeans IDE is known to take a large memory as compared to other lighter IDE's available on the market. The slowdown can decrease productivity and frustrate programmers.
