I read recently that there are about 83 browser variants on OS X. Of these the ones I've used are Safari, Firefox, OmniWeb, Camino and Opera.
Each has strengths. OmniWeb is the only browser to seriously think about the problems with the page/tab UI -- but they went wrong putting the tab/page icons on the left side (one of my machines is an iBook -- horizontal space is at a premium). Camino has an elegant UI and the Mozilla engine, but no Google toolbar. Safari is the prettiest and does the best job with printing and fonts. (Open source products tend to be weak at printing, probably because true geeks never print.) Safari has also always felt pretty fast.
Mozilla Firefox 1.5 RC-2 (Development Information) is a very impressive contender. I use it more and more. It's very fast, faster than Safari on my G3 iBook. The Firefox Google toolbar doesn't work with it yet, but I'm sure it will once 1.5 is officially released. It works with Blogger (Blogger support for Safari is infuriating and abysmal) and at most every site I use (not, however, the AMEX credit card site -- Firefox 1.0 did work there -- I've submitted that as a problem).
Firefox 1.0 was good on OS X, but 1.5 is truly remarkable. It's not as pretty as Camino or Safari, but increasingly it's my preferred browser. Safari is getting relegated to printing tasks.