Your choices are:

Starwood - Sheraton
Marriott - JWM, Renaissance Harbour View, Renaissance Kowloon (used to be called New World Renaissance)
Hyatt - Grand Hyatt

For harborview and location, the choice is clear - Sheraton in Tsimshatsui. Don't know about Starwood rules, but make sure you specify harborview rooms, and their "Tower" rooms are significantly nicer than non-"Tower" ones, from what I've read here and elsewhere. [Note that the hotel is one big building, "Tower" is just to describe their better rooms.]

The JWM is in Central, connected to Admiralty MTR (subway) and a nice mall. Convenient, but you won't get that view from Kowloon looking at Hong Kong Island.

The Renaissance Harbour View and Grand Hyatt are adjacent, and share the large swimming pool, in Wan Chai. Long walk to MTR, and there's again the view problem. The Grand Hyatt should be the nicer of the two.

The Renaissance Kowloon is across the street from the Sheraton, but its rooms have no harbor views. Because of the contruction on Salisbury Road, one has to rely on the pedestrian tunnel to get to the rest of Tsimshatsui, making it a further walk from the MTR, compared to the Sheraton.