I use Firefox for regular browsing. I love its customisation options, especially FireGestures. Oh god I love FireGestures. The only way I can put up with using my PC that doesn't have it, is because the mouse has back and forward buttons on it.
I use Opera and Chrome for a couple other miscellaneous things, like browsing porno incognito
(isn't that what everybody uses Chrome and Firefox for?) and power tabbing.