Having arrived in HK for less than 5 months, I have also visited and seen each of these service studios, my top choice is also EMPIRESTUDIO in CWB. They have a great location, and their studios are larger than there competitors. I understand that they were fully renovated less than 6 months ago, and everything inside the studios is almost brand new, furniture, etc.
After speaking with the other tenants there, I understand that most of them have stayed in the other service studios and enjoy EMPIRESTUDIO much more.
I think their website is www.empirestudio.biz if I recall correctly, go check them out, I hear that they are almost always full. Best value for the money I think.
I lived there for 3 months when I first arrived, now I am in a standard apt with a 2 year lease in Kowloon. Miss the great cwb location.