Google Chrome has recently become my default browser. When developing, Firefox still takes the cake due to my dependency on the Firebug plugin (though version 1.3 has been a little buggy), and various features of the handy Web Developer toolbar.
As for Chrome, I love its speed and ease of use, but I do have a few dislikes. The (wheel) scroll amount is way too jumpy and there is no way to adjust it – I’ve been using the arrows on my keyboard a lot instead which is not ideal. Also, it can be quite memory intensive, with each tab spawning its own process and consuming upwards of 35MBs.