Good ol' 2 fingers is right. They are all good and you should use what works best for you and what you are comfortable with. In my case, even though I want Safari to be the best browser for me, it is actually third behind Firefox and Chrome. They just work better for my workflow. But I still use Safari plenty when I'm just hoping around the internet or dropping in on message boards.
To answer your question, I think I saw the other day that Safari is used by nearly 70% on OS X, but Chrome is growing at a rapid rate. This was one usage report by one website (albeit a Mac one), so take that for what it is worth.