I don't know what would be best suited for you. You haven't indicated many of the factors which could help you determine well-suited tools
- what kind of testing you wish to perform
- what knowledge the testers possess
- what kind of budget you have
- what kind of schedule you are up against
When performing functional testing of a website, the web server technology is often not very significant. Of more importance is often the variety of browser(s) which need to be considered, and any non-standard UI elements being used.
I currently use WinTask for functional test automation, and OpenSTA for load/performance testing.