For favorite, only Opera qualifies. Its features especially I like (Speed Dial, linking of profiles, etc), although it was initially its speed that got me using it. I just can't see any particularly good reason to use Firefox over Opera, although that may be in part that I'd rather use what comes with a browser than searching for plugins.
Other than that, IE is the one I use most, either IE6 or IE8, for compatibility purposes. It does look like the Accelerators feature of IE8 (basically you can highlight some text and do a whole bunch of things with it on right-click, like look it up on Google/Live Maps or get a definition) might be nice, but I doubt it'll be worth changing browsers for. I do keep Firefox installed, though, for the odd site that doesn't work with Opera or IE but does with Firefox.
Of these, I've also used Safari for Windows, Chrome, Konquerer, Netscape (unfortunately), and K-Meleon. The only one I was impressed with at all was Chrome's speed, but it was sorely lacking in features, so I've left it on the back burner for awhile. Pretty good poll options, by the way - nice to see a poll with good options.