Replying to June and July conditions for Thredbo and Perisher

Hey guys, from a fellow australian to another, i was wondering if you guys could help me out. I am planning on making a trip this summer to sydney, probably in mid june until first or second week of july and i wanted to go up skiing with one of my american friends. I was just wondering when i should go up. My uncle said that the best time is in August but i cant go then. would the first week of july be any better than the last week of june? Also, which resort is better park wise? Thanks guys!!