This thread is STILL alive?!?
For speed, performance, etc.:
Safari is clearly the winner. It renders web pages faster and much more elegantly. Webkit-based browsers just perform better than Gecko. Chrome, another Webkit browser still kicks Firefox right where it hurts despite being beta (for Mac). You can't argue this because every speed, javascript and other performance benchmark places Safari first, Chrome second and Firefox dead last. If you include Opera or IE in there, they replace Firefox as dead last.
The only reason why Firefox is still around is because it has thousands of plugins and runs on all three platforms, Windows, Mac and Linux. It's also the first choice that comes to mind when you don't like IE.