I recommend Dragonair. Their service is fantastic, the frequencies are abundant and if you get to fly J they have nice lounges in HKG and SHA. I have flown them many times HKG-SHA either as a r/t or a o/w.

I believe you can purchase tickets from CX website (Dragonair is a CX subsidiary) but since my trips were last minute I purchased the tickets in Hong Kong through the travel agent my company uses.