Depends. I'm an Aussie who's living in HK for a while now. Hong Kong's weather is actually pretty shit year round in one way or another and the smog adds to the burden. Its not a sunny city by international standards (an average of only about 1900 hours of sun compared to the average of about 2200 per year and most Aussie cities get about 2500 hours per year out of about 4500) By far, Oct-Dec are the best months to visit if you want to feel comfortable temperature and humidity-wise but they are prone to be smoggier as the winds come off polluted China then. If you come in the middle of July and there isn't a cyclone, you're gonna be bloody hot and humid but the smog is at its lowest then, the days are long, and you can get some absolutely gorgeous looking blue sky days then. Visibility is great at that time of year. And the trees and greenery are a gorgeous shade of green. Avoid coming in this month (the dullest of the year - only 3 hours of sunshine) cos it's usually miserable in one way or another (from the smog, lack of sunshine and/or mist and low clouds) and its rarely sunny. Reply back if you wanna know more as you can probably tell I'm a weather geek haha.