Chrome is my first choice because - in my opinion - it adheres to the web standards like no other browsers.
Firefox used to be the best one around. Lately, I have been noticing a lot of issues in how it renders the pages. I never thought in my life that I would have had to create hacks for Firefox...
Safari for Mac is good, but it seems slower than Chrome to me. Is it only my impression? I use it on the smartphone though, it's good there.