Opera is my browser of choice. I could use Firefox, but I find Opera to be faster, and for some reason, I just prefer it. And I don't even use a lot of the built-in features like torrent downloader, contacts, e-mail, notes, chat etc. I've customized it quite a bit, so that the stuff I don't use is gone, and it's now exactly the way I like it. I don't really know why I don't use a lot of the built-in features, because they all work just fine, but I guess in my head there's still this little voice saying "a browser is a browser". Might have to try and change that later on.
Also, I've read that Opera is more secure than Firefox (don't remember where, so don't quote me on this and certainly not fight me on it, because I can't really trust my source when I don't remember what it was), which wouldn't surprise me, because 1) Firefox has more users and 2) Firefox is open source, which isn't a bad thing, I guess, but the securty holes are more "out there". Plus, Opera is Norwegian, which is never a drawback, but by far not the only reason I've been using it for the last couple of years.