I'd not dispute that one member of the Julii gens had a large impact on Roman history, but in judging gentes as a whole, none were more prominent in peace, in war, in popularity, and even in infamy than the Cornelia. In fact, without the Cornelia, Caesar would have been nothing: even two of Caesar's three wives (I recall) were from the Cornelian family (from the Sullan and the Cinnan branches). Heck, without the Cornelia, Hannibal might have left Rome as a mere trading port in the mighty empire of the Carthaginian republic, in which case Caesar would have been a mere Punic toadie.