Browsers are personal and seriously, "best with MBA" ? What type of question is that ? A browser is not better on some piece of hardware.
OS X's best browser right now seems to be Chrome. More up-to-date than Safari on Webkit, leaner, minimalistic GUI, the "task manager", integrated "Firebug" and other dev tools, plenty of extensions (Adblock, Flashblock). Firefox can't compete these days.