I'd have to say Google Chrome. It's really fast, efficient, and gets the job done. But, I will give an honorable mention to firefox, I've used it in the past, and it's a really well done browser, too.
I don't think people know that Google Chrome takes information on what you do, and sells it. It's in their Terms of Service somewhere...But I still use it for its speed.
I used to use something called Shades, a Georgia-Based browser company. It had no limits on anything you could do, and being a small company, it had the capacity to handle anything I could throw at it.