Chrome for personal use, and it's very easy to use the developer tools in reading html, css, js. Also my PC is slow - so it wins in that regard as well. Chrome has a lot of good SEO and web development plugins. For testing stuff prior release for client's approval: Chrome, Firefox, Opera, Yandex, Internet Explorer 9 I think covers most internet users in my country. To see how stuff breaks in old browsers - Safari browser for windows (it's like version 5 or something that is available for download.)
And Tor browser to search for "forbidden" stuff (torrents).