Mobile Device Browser File vs. WURFL for ASP.NET

I am working on a commercial web application that has a separate mobile browser version intended for the more capable devices (BlackBerry, iPhone, Android, etc). I don’t want to do simple User Agent contains style logic and was looking at the various detection libraries. It seems like WURFL and Mobile Device Browser File are my best options.

Why should I both Unit test AND Web test (instead of just web test)?

My current position is this: if I thoroughly test my ASP.NET applications using web tests (in my case via the VS.NET’08 test tools and WatiN, maybe) with code coverage and a broad spectrum of data, I should have no need to write individual unit tests, because my code will be tested in conjunction with the UI through all layers. Code coverage will ensure I’m hitting every functional piece of code (or reveal unused code) and I can provide data that will cover all reasonably expected conditions.