There's an interesting article on ArsTechnica ("Macintosh Browser Smackdown") by Eric Bangeman that compares the 9 browsers available to Mac OS X users.
It begins with a presentation of the two main rendering engines used by today's mainstream browsers (namely Gecko and WebCore) and then proceeds to test their load and rendering times for various sites and test suites, as well as their CSS1/2 compliance. Follows a qualitative evaluation with lists of pros and cons for each of the 9 browsers.
The final word is a matter of what suits you best. I personally switched from Camino to Safari early this year, and haven't switched back. The development of the former has significantly slowed down since Safari was launched. I keep IE handy for those few sites on which Safai chokes, or which require IE. Camino comes in handy for the sites that require a Gecko based rendering engine.
A PDF version of the article is available.