On the 12th Floor Concierge, the Atrium Club, both the MK View and Bay Lake View are by request only and cannot be guaranteed. If the MK View is your top priority, you may be better off booking a standard MK View room in the Tower.
With the Tower Club there are a total of 16 rooms, 5 standard rooms and 11 suites: 1 & 2 Bedroom Suites, a Vice Presidential Suite and a Presidential Suite. With the standard rooms, there is no guarantee of a Magic Kingdom or Bay Lake View. However with the Suites , you will be booked into a particular room which will indicate Magic Kingdom or Bay Lake. You will be guaranteed to have that specific room view. There are 4 Standard Magic Kingdom view rooms and 1 standard Bay Lake View room on the 14th floor.
The lounge on the 12th floor is bigger with more seating then the 14th floor concierge lounge. They converted 3 standard rooms into the 12th floor lounge, so there are 3 balconies available on the MK side for all Concierge guests to watch the fireworks. The lounge on the 14th floor also offers seating outside on the balcony, which is something that is not offered on the 12th floor lounge.
Finally both floors serve the exact same foods for breakfast, afternoon snacks, 5:00 PM hors d'oeuvres and 8:00 PM deserts & cordials. The 12th floor Atrium Club is less expensive then the 14th floor Tower Club, even though on both floors offer the exact same service. The 14th floor is more expensive because fewer number of total rooms and Suites.