When in the office I actually use three different web browsers, but my main browser is Google Chrome.
If you are not using it, you really should take a look at it, it is fantastically quick to load pages, easy to use and the URL bar searches Google automatically!
Now I am not going into details on all the differences or debate which is best but I just wanted to pass on my opinion as an everyday user of it. I religiously used Firefox before but since I use Googlemail/Google Reader/iGoogle and more Chrome just fits into the package really well.
I came across the following promotional video on TechnoBuffalo and I like it because it is a really fresh depiction of how fast Google is.
Let us know which browser you use and why, by leaving comments.