not possible to answer without knowing your preferences. What is important for you.
Read the reviews already I assume?
I've not stay in either of them but Rosedale Causeway Bay is the better locations for local/international brand/chain shops and restaurants also Causeway Bay MTR is only a 5 min walk away. Rosedale Kowloon is actually in Tai Kok Tsui 15 mins walk to Mong Kok MTR or 10 walk to Olympic City MTR.
Rosedale on the park is in Causeway Bay with slightly larger rooms but older. Rosedale Mongkok is in Olympic (Tai Kok Tsui). It is a newer hotel but I normally would not recommend due to its location. Since you are an experienced HK traveler I don't think you would mind Rosedale Mongkok
Ever decisive, we have made a booking at the Cosmopolitan
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