Hi Deborah,
When I told my sons (two of whom are teens) that I booked the
Grand Floridian for a future trip, I got lots of moans and groans. They feel the resort is too girly & flowery. However, they do like both of the pools. But if they had their choice, they'd pick the
Contemporary Resort. I don't think it offers anything differently, but for them it is more masculine with its modern design and monorail running through the building. Overall, they are more comfortable there.
Also, August is a rainy month; you may find the Contemporary with the rooms housed in one building may be worth it if you get caught in the rain rather than the Grand Floridian with its buildings spread out.
Have you had them look at the pictures of the resorts? Perhaps they could do that and their reactions would help with your decision-making.
Regardless, they are both fabulous resorts and in the heart of Walt Disney World!