In general, southern uses more vegetables, and romano cheese! Northern is heavier and creamier, and parmesan.
Sicily, which is very south is also a little different, their recipes are very "olive" based.
I grew up with a great grandmother, Nonna, and a grandmother, Nana, and another grandmother, Nonni. All three came here from Naples - purely coincidence. My Nonna and Nana were further south in Naples and my Nonni in the northern part. Just that little difference in areas made their cooking styles completely different. Nonni's food was a bit heavier, Nana and Nonna were spicier.
It's a great question and there are many answers. No matter where you go in Italy, the food is fabulous but like anything else, it's a personal preference, which you like more.