It’s been some time since I travelled to HK regularly. Best carriers were always Singapore and Cathay Pacific and if I was travelling now and paying myself I’d seriously consider their premium economy options, comfortable seats and far better value than business class. Virgin also offered a very good service but no longer operate out of HK as far as I know. Any time is a good time to visit HK but the rain season is May to Sept, with June to August being the wettest. But it’s “nice” rain, not like the miserable stuff we get !!