Firefox here. I have IE 7 or 8 installed (can't remember). I did try the new google chrome for about a week or two. Since it was still in beta at the time, I was a little worried about security, so I switched back to firefox for the time being.
I have IE, Firefox and Chrome. Default is Firefox because its addons are very good and useful. Chrome however is very fast (actually the fastest I found) but does have all the features Firefox has.