Rakdos, Gruul and Golgari are all around equally great in my eyes. Boros and Orzhov have their moments too, but especially as of the current block Boros has been shafted. I also kind of quibble with the Gruul being flanderized into no-tech cavemen running around naked rather than a bunch of angry scavenging anarchists looking to blow shit up, but that's a fairly minor quibble.