Why, Opera
Opera is my browser of choice.
It has a lovely interface, with different selectable skins. More importantly, it seems more responsive on this MacBook than either Firefox or Safari. Safari in particular seems sluggish in comparison. Chrome may be okay, but Google can get back to me when they decide to use a graphic artist for the interface.
Firefox is a secondary choice in instances when media plays better, or even at all, compared to Opera. It seems Firefox will do anything, which sometimes Opera will not, but subjectively this seems to be improving. But I still prefer Opera. Firefox is innovative, however, with one new nice feature that of 'Personas,' which allow one to easily choose from a wide array of artistic styles for both header and footer of the browser window. If a small thing, still quite nice.
Something more important could be security. If they all boast of this, subjectively I lean towards Firefox, if doing online shopping, for instance. But another may be as good or better, they have all probably had their issues, and possibly leapfrog each other to one degree or another. Any more it seems one can receive a vast array of Cookies from sites visited, or third parties, with some of them necessary, and many more better gone. Managing such things varies from Firefox to Opera, etc., so surely some personal preferences involved.
Power users may have different criteria, and I hardly utilize all the many features available. I tend to be happiest with a modern browser that is updated periodically, is nice to look at, and is responsive. Opera provides all that.