Firefox is the browser option for me, mainly because of Firebug. Safari (or in particular the WebKit nightlies) would be my choice due its speed if I didn't have to use my Firefox extensions.
Opera, in my opinion, is a useless browser. It almost has as many quirks as IE but is used by far less people. I wouldn't be concerned if it was removed from existence

IE..... you can probably guess my opinion here lol