Username or EmailPassword
I decided to be contrary, and write this note with Konqueror 3.2. I have both Firefox and Mozilla's Seamonkey. I also Purchased Opera 8 beta.
It is hard to emphasize the advantage that Firefox has over the other browsers, because of its use of extensions. Some key extensions (like Adblock) also run on Seamonkey, but Firefox's entire interface is geared to these things.
I like Opera in many ways, but it falls down on certain Web sites (The Register comes to mind), and the complaints people have about Konqueror being too complex and too configurable applies to Opera in spades. In addition, the font rendering under Debian Linux leaves something to be desired.
What are some of the things I like about each: All are fast, but Opera is fastest on rendering. All do tabbed browsing well, but Seamonkey and Firefox with the Tabbed Browsing extension do best. Opera edges out Konqueror when it comes to quickly replacing a Web site's style sheet with a user one. When it comes to page rendering, the Gecko based browsers win. Add the User Agent Switcher, and there are few sites that won't work with Firefox.
A specific comment on speed. One poster complained about Seamonkey's slow performance. That individual hasn't used the browser in a while. It is actually quite nimble.
If I had to make a personal ranking of the browsers so far, it would go something like this:
I would be pretty happy with any of them.