I have Safari, Firefox and Chrome installed.
Generally, I have used Safari. It has never hesitated to load anything for me, and my bookmarks are kept in sync on 4 Macs using Mobile Me. I have never liked Firefox, but only because of the aesthetics and UI. It has had the great advantage of some cool plugins, such as grabbing flash video and downloading it to your drive. Safari 5 not has plugin extensions, so that advantage is gone.
Chrome seems good, but offers me no advantages over Safari.