The 51-year-old believes the two perennial rivals are the league's most complete sides, while he touched on his bust-up with Adem Ljajic and plans to reform Italian football
In an interview with Corriere dello Sport on Wednesday, the former Lazio and Lecce boss explained that the superiority of the Supercoppa pair sees them lead the way in the Italian top flight, and gave special mentions to Fiorentina, his former club, and Roma.
"The two most complete teams I have seen are Juventus and Napoli," Rossi said. "They both followed a strict philosophy.
"Napoli took a certain type of young player, and that will come in handy not only now but also in the future.
"Juventus have always targeted players who are already 'built'.
"Fiorentina did the only thing they could do - initiate a total revolution. Roma have also recruited well."
Rossi was sacked by Fiorentina in May following a much-publicised conflict with Adem Ljajic in a 2-2 draw with Novara, where he proceeded to punch the Serbian midfielder, but while the trainer accepts his actions were misguided, the context should not be underplayed.
"I miss the coaching aspect; seeing young men grow day by day. Sundays were the result of what you did [in training] during the week."
"I did something bad, which is not to be repeated, but it was at least understandable, if not justifiable, in the heat of the moment.
"I repeat, I am wrong but the fact remains that the bitterness has given me a certain ease of judgment. Personally, I avoid jumping to conclusions without knowing the facts."
Rossi then covered a wide range of issues currently affecting the development of Italian football, and identified long-term planning and the downsizing of professional leagues as to what is needed to boost calcio's prospects.
"It has become a necessity to sign young players. Economic difficulties have led to a focus on players with lower salaries," he pointed out.
"For budgetary needs, our football requires a thorough reform. We should reduce the number of professional teams, and introduce a system for semi-professional clubs.
"Serie A and B should cut down in size, while Lega Pro should only have a couple of divisions.
"Seventy or eighty professional teams are more than enough. And then if you really want to focus on young players, then you should also start looking at the youth leagues."