Since the Firefox craze started to bloom, I've been using Firefox. I just use it specifically because it has tabbed browsing and just overall a much more comfortable package when browsing the web. Because with IE for example, my computer could accumulate dozens of spyware cases in any given day, and I really hated to clean that crap up. Not to mention IE just has felt 'exploited' on the web, and you get an aura of popups and silly tricks to screw you up. Even with IE addons made to prevent these things, it still feels like poo.
I've tried my hand at Opera, but having used Firefox before that ruined any chances I would switch to that browser. Firefox suits me at the moment.