I can report back on YHA Mei Ho House Hostel. The twin room looks exactly like this (we had two different rooms):
http://www.yha.org.hk/eng/meihohouse..._room_standard
It's clean, simply furnished, with a minimalist modern look. The twin beds are comfortable enough. You get housekeeping every 3 days. There is a kettle. The room is definitely on the spacious side for Hong Kong (25 m^2).
The bathroom is in good condition and everything works well, with a comfortably sized shower stall. You have access to a self-serve laundry and microwave. The included breakfast is simple, and offers three options (Chinese, Hong Kong, and Western). Its value is listed as about 30 HKD, and I think it's worth that.
You will end up taking the MTR a lot, of course. But my feeling is that unless you are staying right at TST or Central or Admiralty, you will have to take public transport a lot anyway, and the extra few minutes from Sham Shui Po as opposed to say Mong Kok doesn't really matter, once you have done the work of getting into (and then out of) the MTR.
I liked the Sham Shui Po neighborhood. Lots of interest in the small shops and markets and shopping malls.
The fact that this place has hostel in the name undoubtedly keeps some people away, which is probably just as well, as it is a fantastic deal if you want something other than a dingy cell to sleep in.