For me, I choose as follows:
Firefox - My main browser for pretty much all my surfing. With the Ad-block plus plug-in to save bandwidth, it’s definitely the quickest on a slow speed mobile Internet connection.
Internet Explorer - Testing purposes only. I only use it if the PC I’m using does not have any other.
Google Chrome - My preferred on a mini laptop (Netbook), as due to the 600-pixel display height - gives almost the viewing area as using Firefox with a toolbar on a larger 1024x768 display.
For comparison, the following shows how the headers compare between the browsers with optional toolbars and IE menu turned off, in the order of Firefox 3.5.3, IE8 and Chrome 3: