You have "runs on actual browser" as a pro, but in my experience that is a con because it is slow. But what makes it valuable is the lack of sufficient JS emulation from the non-browser alternatives. It could be that if your JS is complex enough that only an in browser test will suffice, but there are a couple more options to consider:
HtmlUnit: "It has fairly good JavaScript support (which is constantly improving) and is able to work even with quite complex AJAX libraries, simulating either Firefox or Internet Explorer depending on the configuration you want to use." If its emulation is good enough for your use then it will be much faster than driving a browser.
But maybe HtmlUnit has good enough JS support but you don't like Java? Then maybe:
Celerity: Watir API running on JRuby backed by HtmlUnit.
or similarly
Schnell: another JRuby wrapper of HtmlUnit.
Of course if HtmlUnit isn't good enough and you have to drive a browser then you might consider Watir to drive your JS.