I've been using Mozilla. I don't really like it, but I've been using it more as a case study then anything else. I recently reformatted and wanted to save myself the aggravation of new spywares. Not that it seems to be helping. I still got a couple.
I don't really get why everyone says its so fast. Sometimes it times out. Sometimes it also takes a long time to load background images depending on things, but that's java related I think. I think all three (Opera, IE, and Firefox) are good enough now that it is a matter of preference then performance.