The best time to travel to Hong Kong
I was never a girl who will check the weather and seasons before I book a flight. Until there was once I purchased flight ticket to Japan during a promotion, then I found out the traveling period was summer with a lots of rain. I have no choice but pack my luggage with a small umbrella (which then found lost, I doubt I did put it into my luggage). Anyway, we were luckily to have good weather in Japan just 2 rainy days out of 6 days. But I learned a lesson to check on the weather before I book the flight.
No matter which country, Spring/Autumn always the best seasons to travel. But these period tend to be the peak traveling season, and you have to pay more for flight n accommodation. Unless you wanted see some seasonal flower/plant, otherwise I will advice you to pick end of Spring/early of Summer/end of summer, where the weather will still good to travel without high expenses.
Bear in mind to check the date of Chinese New Year (which is different every year, and usually fall on February), where a lot of people to flock in to Hong Kong and making a peak season. But if you wanted to join the festival season of Chinese New Year, visit there a few days before Chinese New Year, as most of the shop will close during CNY.
If you were a cultural/festival lover, you may need to click on the following link to find out more,
Hong Kong Discount Season (Shopping Spree)：December －February（Christmas & Chinese New Year Eve），July – September（Summer discount）
Not to forget the public holiday in Hong Kong, you will never want to join the crowd to Lantau Island, which will take you about 2 hour for a cable car.