IE8. Firefox and Chrome suck. I'll never use FF again, after it decided to take over my system, peg the CPU @ 100% and eat up every scrap of Ram. Chrome will keep re-installing un-needed crap when it "updates", and if you remove it, it leaves crap behind in the Registry causing IE to have issues, primarily when trying to open links that are embedded in e-mails.
There is NOTHING wrong with IE. As long as you dont install crap toolbars (Google's toolbar is notorious for making IE unstable), IE is rock solid. I've never had any problems with it, since IE6 or so. When you start adding addons to FF, you negate any "advantage" it *might* have over IE.