Having used both (and Ruby’s Capybara), I prefer wallaby since the APIs are really close. Hound is also cool, just I’d have to learn different API ;).
I believe that these use webdirver (or the new Selenium 2 should be sort of supported by now too). So you can hook up any selenium-supported browser to it. You can also use phantomjs, but I believe this project is being abandoned in favor of headless Chrome.
