For the Century and Kowloon Novotels, the lounges are small, and you'll find better breakfast at the main restaurants so definitely head downstairs with the masses if it is available to you.
It seems to be very difficult to book a standard room in Century - they seem to permanently occupied by various mainland tour groups these days. If I remember correctly, the standard room gets the bathtub + normal shower, while superior rooms don't have a bathtub, but has the rain shower available. Even as a silver, I get upgraded from standard to superior quite often. However, for both properties, I never get to see the exec floors unless I use some cash. Obviously, experiences may be different for plats.