Google and Apple are EVIL, so Chrome and Safari are only there to test some websites.
Firefox I use most, mainly because I loaded it with add-ons. The search plugin collection of MOZDEV is unmatched, and Greasemonkey, Adblock, Webdeveloper, UASwitcher, Ghostery, Downloadthemall etc are really nice plugins.
I use Camino a lot on my old G4 mac, and Opera/Tenfourfox if I want the fancy HTML5 stuff on a G4 mac, since almost noone compiles for PowerPC any longer.
I use Safari to grab stuff hidden in Javascript or Flash, since its activity console gives you URL's to ANY content. There is nothing that can be blocked from Safari to download!
Last I use is Paparazzi, as it allows you to render webpages at 10000x10000 pixels, very nice for Google Maps.