I don't use the internet, the internet uses me. It does this to everyone. People just think they are controlling it.
No, but seriously, I use basically all of them. I primarily use Firefox due to its extensions. But it's getting damn slow and bloated even in its clean status. Chrome is a nice upcoming browser, but has some work to do before it's ready for mainstream use. IE I have to use for my online job, despite my dislike of it. It's the corporate option, so i'm stuck with it. Opera I don't mess with as much as I should, seems quite good.
By the way, Firefox has really managed to piss me off lately. Besides the crashing bugs that seem more common than versions before 3, there are some tab glitches i've run into with the Google toolbar. I fixed one of them, but another is still present where the tab will never close if you press X. And then it gets sluggish after a few weeks for no reason (clearing cache and such does nothing).