Dolphin for me, does everything I want it to do. It doesn't have a static address bar like some - meaning it scrolls up with the page rather than stays there all the time wasting screen space, has it's own bookmarks so I don't have to see the stupid non-deletable (unless rooted) 3rd party bookmarks the vendor includes, has the bookmarks pop-up when I hit menu (not so with the default browser and having it makes it easier to use one handed), has Flash unlike Chrome, scores nicely on the HTML5 test site, etc.
No reason to use anything else so far... and I've tried them all pretty much. Firefox is my preferred for my home Ubuntu Linux machine, but not on my phone unfortunately.
Rev,