Gentlemen, gentlemen, no need to shove. Opera - and this is coming from a true-blue Opera user, remember - has a plentiful supply of quirks: quirks that to the non-devotee are infuriating. Internet Explorer has fewer quirks but vast gaping security holes you could drive a truck through, and a severe lack of modern features.
Opera is like French cars used to be. Lots better than most at the things it's good at, weird and downright stupid at others. You either love it or you hate it. With Opera there is very little middle ground. Oh, and it's good at blocking pop-ups.
Explorer is tolerably good at everything except security and doing what you want it to do (as opposed to what Microsoft wants it to do or (worse) what some damn spam-pusher wants it to do). Popups and its inability to deal with common user preferences destroy it as a usable, pleasant product. For example, if you chose not to install Flash, IE insists on putting up a click-window on every single damn page you ever visit that has Flash complaining about it. (Specifics vary: with some versions on some OSs you can get rid of this, but there are plenty of other similar bugs.)
Mozilla is, objectively, the best at almost everything. Best security (bar maybe Opera?) best pop-up blocking, most compatible, by far the most stable. But it's ugly. No matter what they do with it, it still looks mega-clunky.
I can live with that.
Which do I use myself?
Depends on the site. Mostly I use a different browser for my three favourite sites. IE 5 or 6 at Storage Forum, Opera 6 at Wikipedia, and Mozilla here at Bird Forum. I keep all three open most of the time. Sometimes I visit a favourite site with the "wrong" browser and get quite confused when the browser does something I didn't expect!
But if I'm just surfing around, I practically never use IE: it's just too much of an invitation to the pop-up pushers and the spyware vendors. At sites you don't trust, always use Mozilla or Opera.