Opera is the most standards compliant browser...but how many of you really use it? And IE8 is really more standards compliant and Microsoft is really going the "standards way" these days...
More standards compliant than what? IE8 will still be 10 years behind all other browsers in standards compliance when it comes out.
I perfer FireFox as well, I test my site in both IE and FF though since they are both the most widely used browsers on the net