Who will win? So far, FireFox 3 wins. Internet Explorer is still in its beta phase, and I found thousand of bugs inside it. If you're not a web developer, stay away from IE8 Beta 1 until its final version. Stick with FireFox 2 too if you don't want to face memory leaks as in FireFox 3.
I recommend FireFox, once again. Power it up with Adblock Plus, Flashblock and NoScript.