Firefox for me. Cant see it changing for a long while. I just cant live without AdBlock, NoScript, Webmail Notifier and several other goodies that I cant get with any other browser. (not all together anyway)
It's fast, has crashed on me only once in as long as I can remember and has all the superb plugins/extensions.
I have Chrome and Opera as well but they just don't offer what Firefox does.
IE will forever be the spawn of Satan no matter how much they improve it. The damage was done a long time ago and I'll never go back to it.