Firefox ftw! :P Even though it's quite good at eating some memory. As others I tried Chrome, and it is quite good, but obviously missing the customization of firefox, which I can't live without :D
I don't even understand why people would touch Internet explorer... even with a ten-foot pole. Unfortunately I have to when developing websites as it's kinda the mainstream browser in the industry for bigger companies .__.
Trying out the Acid3 test in IE is just embarrassing, I scored a 12 :P And actually Chrome did better than Firefox. Chrome scored a 100 while firefox landed on a 93.
I would change to Chrome if some sort of add-on support was added in the future. Don't know what kind of plans they have in that area.