Sierra Tower is the best with a great view of Downtown Disney & glimpses of Disneyland & California Adventure looking out to the east. Looking to the west, you overlook the Neverland pool & the DL Hotel grounds - also nice.
Marina Tower offers a city view to the north. Some of their rooms can also see the fireworks from Disneyland. Looking to the south, you overlook the DL hotel grounds.
Bonita Tower offers a view of the waterfalls & pine trees to the north, with glimpses of the DL Hotel grounds. Few rooms that are on the east side of the tower can see the fireworks & glimpses of Downtown Disney, Grand Californian Hotel, and California Adventure. The view to the south is parking lot & city (least favorite view).