We didn't have a car, in Sicily so I can't really answer that - or compare the two as we did have a car in Crete. It was a long way from the airport (Catania) to Taormina and the taxi quite pricey, but we had no trouble doing a couple of day trips from Taormina to Mount Etna and the surrounding area by tour bus. Sorry I can't be more help on that one

Didn't get 'hard to navigate' if it means easy to drive, no more problem in sicily than elsewhere in europe. Small roads here or there, so don't take a big car.
Crete is also easy to navigate... with smaller roads from time to time.