What is the best way to test my webforms applications?
Looks like people are loving Watin, and selenium.
I'd go with WATIR (Web Application Testing in Ruby) - http://wtr.rubyforge.org/. We (Acsys Interactive) have been using for about a year and the tool is great.
I developed a simple wrapper in .NET so that I can execute my WATIR scripts from Unit tests. The framework is incredible and you have entire Ruby power behind you. There's support for Firefox & Safari (FireWatir project).
It's very similar to WATIN (in fact I think WATIN was inspired by WATIR) but I find that WATIR community is much larger than WATIN one.
There're test recorders out there that you can use and tons of tutorials.
It's really your choice. If you feel like the tests need to be in .NET and you don't want to support any other language then your choice is WATIN. On the other hand, if you want to try a fun and quite powerful scripting language (that's what Ruby is) then go for WATIR.
Question to WATIN guys, does it support FireFox/Safari?