For me Safari was first choice on Snow Leopard. Then they brought out the 5.0 update and utterly massacred it - so i went to Opera.
Now on the new MBP I'm running 10.7, so I'm back on a working Safari again, and so far its still my favourite browser.
that said, Opera is now my favourite browser on everything else, which is weird. I use it on Windows and my iPhone aswell, and i always use Opera for any video streaming online (because the adblock is far better).
I usually have Firefox lying around somewhere, for troubleshooting mainly - but i barely use it.