Here is the differences between both floors that I wrote about on the Contemporary FAQ thread.
Both Club Level floors offer service which includes personalized front desk and guest services, turndown service, refrigerator, coffeemaker, and lounge with continental breakfast, midday snacks, evening wine and cheese, beer, and evening cordials and dessert. The Atrium Club is on the 12th floor and is comprised of standard rooms and has full Club Level service. The Tower Club on the 14th floor offers the same full Club Level service. When you arrive tell the Cast Members working at the bell services desk located outside you are staying Club Level. They will call another Cast Member escort you up to the 12th or 14th floor because they already have a key which is coded for either floor that needs to be insterted into the elevator, so once you arrive on your floor you can check-in up there.
Difference between the 2 Club Level floors
The Atrium Club Magic Kingdom View and Bay Lake View became available by reservation on 01/09/09. Prior to that all you needed was an Atrium Club reservation and you would end up with either view.
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 view which will indicate the Magic Kingdom View or Bay Lake View. Finally there are 4 Standard Magic Kingdom View rooms and 1 standard Bay Lake View room.
The lounge on the 12th floor is bigger with more seating then the 14th floor Club Level. They converted 3 standard rooms into the 12th floor lounge, so there are 3 balconies available on the MK side for all Club Level 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.
In the 14th floor rooms their mini fridges will already have cans Coke, Diet Coke, water and apple juice. The mini fridges for the rooms on the 12th floor are not stocked like the ones on the 14th floor, however anyone staying on the 12th floor can always take those items from the lounge themselves and put them in there.
The balconies in the rooms and the lounge on the 14th floor are bigger then balconies in the rooms and lounge on the 12th floor.
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.
Finally here are links to pictures of both lounges.
http://contemporaryresort.net/atriumclub.html
http://contemporaryresort.net/towerclub.html