Due to the various pros and cons of each KW TS, I doubt there is a "Best".
I would agree on Jeff's comments and add the following:
Banyan is a group of renovated homes that have a common garden and pool area. The reno home is why no 2 units are alike. While the pool and spa are secluded and nice, they're not very big. Old Town location is great for Duval activities.
Galleon seems to get mixed reviews - some love it while others say the rooms are worn out and dated. Not sure of the total number of units (by reading another thread, I'm sure timesharemogul could provide that info) but it is a larger property. Maybe that's why the room view reports range from "great" to "stinks". Again, Old Town location is great for Duval activities.
Sunset Harbor is Hyatt's 1st TS property. The room layouts vary, some 2 story townhouses and various 1 floor 2 bedroom floor plans with lock offs. Nice pool area to watch the cruise ships come and go. The units are not the sexist of the 3 Hyatts in KW, but the view from the 2nd and 3rd floor units can not be beat. Due to its Old Town location and views, it is the most desirable Hyatt in KW (can be a little pricey).
Hyatt Beach House has nice units, all identical 2 bedroom and no lock offs. Nice pool area and small beach. In general, the lowest price way into the Hyatt program. If you are going to travel to other Hyatts, its hard to go wrong with Beach House. Some people like that its out in New Town and away from Duval - but if you're going for the Duval activities, its not the best location.
Hyatt Windward Pointe has the nicest and largest units (understatement - granite countertops, stl stl appliances, really large master bath). Again, all identical 2 bedroom and no lock offs. Nice pool and spa area. Note that this is an RTU property - expires somewhere around 2075 - not that that is a huge issue, but just wanted to make sure you are aware of that. Same thing as Beach House, its in New Town. Some say the location next to the airport drove them crazy while others say the planes didn't bother them at all.
Coconut Mallory is out in New Town and is on what appears to be a down hill slide. Its units and location are not real desirable - probably explains way they are the cheapest weeks to buy.
Coconut Beach Resort is a nice property with decent location down by Casa Marina at the Atlantic end of Duval. While there is a selection of shops and restaurants nearby, most people who want Duval opt for the lower end of Duval (Banyan, Galleon and Sunset Harbor). Not sure of Coconut Beach's affliation, but similar to Banyan and Galleon, your trades are done thru RCI or II. If you go with a Hyatt, you can do internal trades to other Hyatts as well as trade through II.
Will you be staying the same week each trip or will your travel times vary thru out the year? The rule of thumb I'd suggest is that if you will be going to you home resort half of the time, buy at that property. Note that if you buy a Hyatt, you are guaranteed your week and your deeded unit. If you plan on going to KW alot, then research which week/unit it is you're going to purchase.
While we have our favorite, there is no clear cut winner for every person's situation. So I say rent a unit or two and test drive them before you buy.