The Camino™ Project
I use Firefox on Windows. Great browser, though until web sites get caught up it's very helpful to have the "open in IE" extension.
On OS X I mostly use Safari. I like the fonts and readability, I like the compact use of space, I like the OS X services integration. I also use Firefox, but the font/layout is not appealing. I like Omniweb's ability to visualize the windows/tab tree and manipulate it, but horizontal tabs don't work on an iBook display.
The biggest drawback of Safari is market share. It gets support out of proportion to its market share because of the "Mac Factor" (OS X use is much higher in geeks than in the general population), but it's definitely behind Firefox. Blogger has a terrific wysiwyg-like HTML editor (Compose), but it's only available in Firefox (yeah, IE too, probably Mozilla but I don't use Moz).
Camino 0.82 is a cross between Firefox and Safari. It's the browser that Apple should have gone with. It's really very elegant. I tried it out on Blogger, but I got the old HTML editor -- not the new Compose editor. Better than what I get with Safari, but it's not 'Compose'. I think Camino uses an older version of the Gecko, so there's hope that when it gets to release 1.0 there will be a Mac browser with the web constituency of Firefox.