I use Safari when I'm on Mac and Chrome when I'm on Windows. Since OSX is my primary operating system that would make Safari my primary browser.
I gave up on IE years ago, back when dial-up was still prevalent. I was tired of IE crashing and losing all my open windows, and I really appreciated the tabbed browsing features that the other browsers offered. I was a longtime fan of Mozilla, and then Firefox back when it was called Phoenix, and later Firebird. I've since moved away when Safari caught up (no more rendering bugs) and when Firefox was no longer the nimblest browser. I've dabbled with Opera but never made it my primary browser until my much older Mac couldn't handle the Safari 5 update: because Opera is so nimble and lightweight it is ideal to run on older machines. I really like Chrome's forked process system, as it is so much more responsive and doesn't get bogged down by Javascript-heavy sites like the other browsers, but the user interface is still bogged down by small bugs and lack of attention to detail on the Mac version.
I've given dozens of browsers a shot over the years, some of the more interesting ones being iRider, GhostZilla, Dillo, Flock, Camino, OmniWeb and Amaya, but these days I find Safari suits me best: a snappy rendering engine, excellent keyboard shortcuts, and fastidious attention to details.
For instance, one thing I like about Safari that no other browser does is truncate the names of tabbed pages: If you have a lot of tabs open and they all start with the same text, it'll recognize that and only display the useful part on the tabs.
Browsing Netflix: Firefox 4 beta on top, Safari 5 on bottom