Catania is the closest International airport. From there you can take a bus to Modica (about 3 hours) or drive (about 1 ½ hours). The train requires a transfer in Siracusa.
A car is ideal if you’re planning to visit some of the smaller villages in Sicily. The bus is a good option as well. People often complain about train service in Sicily because some lines to small towns are outdated and slow. And, some of the train stations are outside the center of town by 1 km or more. That said, I’ve found the trains to be pretty reliable.