Firefox. Chrome's a bit too simplistic for me, so despite being slightly faster than Firefox, I can't bring myself to use it. Plus, I value my privacy, and Google is the last entity on earth I'd trust with that.
And IE? Get the fuck out of here, I'd have all of about 5 pixels to view a page past the ten spyware toolbars that come pre-installed on a factory computer. And even when that issue is taken care of, it's junky and slow, even at its most streamlined; the difference between IE and Firefox is not unlike the difference between a slingshot and a hunting rifle, respectively.
My sister (who happens to be excruciatingly computer-illiterate) uninstalls Firefox from the family desktop every time I put it on there because "it broke the computer" by becoming the default browser. I tried explaining that she could import her settings instantly and have every last one of her old settings, down to the bookmarks, but she staunchly refuses to use what amounts to the same damn thing, only improved in every way imaginable.
When you clearly observe that my dinky bottom-shelf netbook loads a page instantly on Firefox, while the monstrous quad-core humming silently in the other room (which can smoothly play HL2 on full settings at 1680x1050 resolution with very little help from the shitty media card that came with it) chugs along for a few seconds before it starts to load a page in fragments on IE, and you still argue that IE is superior, I'm afraid I reserve every right to be condescending and shitty on all matters computer-related. Now, whenever I walk by her surfing the internet, I feel like she deserves to have to stare at a blank, white screen for five seconds every time she clicks over to a new page.