I've been to Perth but not Sydney. The city is pleasant and clean but not a great attraction in itself. Fremantle also has a certain charm, and the Indian Ocean beaches and sunsets are great. I rented a car and drove around the Margaret River region, which is a wonderful combination of beaches and wine country. Also went down to Walpole and Denmark Beach. Walpole has the canopy tree walk, which was interesting. Seeing kangaroo by the roadside like you'd see deer in the U.S. at night was also a thrill. Driving distances can be substantial, but the region is rich in natural beauty.