I have packaged apps up using Inno Setup before and highly recommend it. It is a straightforward tool and is much simpler to use if you also use ISTool (http://www.istool.org/). ISTool gives you a GUI for writing the Inno Setup installation scripts. This gets you up and running right away without having to learn the details of the installer's script syntax. You can literally put together your basic installer in 10 minutes.
The Nullsoft tools are powerful but they use a custom mini-language. If you are willing to learn how to use that or learn how to plug other languages into the system then they may be good choice. However, unless you need some fancy data munging or processing during your install I would recommend Inno Setup and ISTool as a much faster way to build a Windows installer.
