Selenium Question:

If you like your test cases in Ruby (or maybe .net) and are willing to
dig through "hard to understand" documentation - then Watir is a tool
for you.(if you are perl/php/java shop - don't even bother considering Watir
for now)
Watir does have advantage that its recorder uses IE to record.
With Selenium - if your site does not work with Firefox - you will
have to manually write the code(not big deal)..

But the biggest advantage of Selenium is its support for FIT HTML
and the vast languages/browsers/platform that it supports.
(with good documentation)
But maybe things may change in future.