Personally I find Firefox (3.0.5) painfully slow, not really good looking (unpolished) and its UI is buggy on top of that (radio buttons and checkboxes). Fonts don't look as good as they could either.
Internet Explorer is a little faster but its UI layout makes it look like "hey we got a cool UI, ehrm... where does the old-style toolbar go?". But it's got actually pretty helpful XSLT error messages, is slightly faster and ... actually more secure (it is better at detecting malevolent sites), though.
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