Opera, I used Firefox for a while but something got screwed up and it ended up taking about 5 minutes to open each time, which drove me to the brink of sanity. (When you become really crazy, your sanity loops around and you become completely sane, which is boring.)
Since probably 2006, I've mostly been using Firefox.
I'm currently using Firefox 3.6.10, and on February 8, 2010, not only will Australia get the release date of the 3DS, Firefox 3.6.11 is released.
Firefox 4.0 is scheduled for release later this month, and already just a few months later, the next MAJOR release of Firefox, currently known as Firefox 5, will be released mid-2011.
Currently using Firefox 4.0b10 on this computer, Firefox 3.6 on my other. I like it because of all the addons and themes available. I occasionally will use Chrome, but not really.
Took a look at Rockmelt, it seems interesting but even though I'm on Facebook a lot, I don't post much with it.