Dave covered the basics well. I'll just add the two experiences are very different. The Atrium Club is the 12th floor, the top floor of the atrium - so open to all the noises and such from below. The rooms are the same theme as the rest of the tower rooms below.
The 14th Floor/Tower Club floor is totally self-contained/not open to below and it's effectively like staying in a totally different resort. The floor decor/design is different and the rooms - even the few non-suite rooms - have a different size/design/layout than the rest of the building. Still Incredibles-based, but they look nothing like the normal rooms.
The 14th floor has over-sized (read, huge) balconies relative to the 12th floor/rest of the building.
Both lounges have a balcony that faces MK and they pipe in fireworks audio - this is great because you can have a Bay Lake facing room (cheaper) and still have the lounge to go to for fireworks.
IMHO Tower Club is more of a splurgy type experience if you find value in the larger room sizes/balconies/usually quieter/more personal lounge. Atrium Club would be the more value alternative - still the great CL lounge offerings/amenities and CL CMs, just a larger guest count and prone to more crowdings during the ebb and flow of the day.
That said I'm a fan of both and can make a case for/against either depending on what someone wants out of a trip. Happy to answer any questions.
