If we talk about the program, Opera wins by 20 miles. Thesuite already comes with everything you need, and some things you don't :D but still, its speediness, standards support and visual consistency make it a plus.
Firefox is a good browser, only when it has the right extensions installed. A bare, no extensions install of Firefox is pretty much like saying IE done right. If it weren't because all those extensions make Firefox more slow, laggish and insecure, it would win the browser wars.
In my personal opinion:
Firefox + some DECENT extensions > Opera > Firefox > Safari et al > Links IE 5.5 > browsers coded by monkeys > other IEs
I'm truly AMAZED noone's mentioned Netscape Navigator, Links or even Mosaic. I mean, come on, some sites are just fun to see in text mode, and it's really amazing to see what real content do the sites have without all their Flash and Java crap (have you tried BBC's?)