What do you consider nice?
Nicest would be California Grill, Jiko, Artist's Point, Flying Fish, etc. But a meal for 10 will set you back maybe $800 - possibly more.
Kona is a great value in terms of type of food for the price.
Spoodles, Whispering Canyon, Ohana etc. are all fun places. The food and atmophere is less "fancy" and so are the prices.
I personally think buffets are hard with a crowd. But I'm not a buffet fan.
These are all hotel restaurants. Downtown Disney would give everyone a chance to do a little shopping and strolling as well (though I'd rather go resort gawking)
My own two cents would be to pick one of the Boardwalk area restaurants (including the Y&BC and Swan/Dolphin). You can spend some time hanging out around the Boardwalk, maybe catch part of Illuminations or the Fantastic fireworks from the bridge between the BW and the Dolphin. There is often street theatre in the evenings on the Boardwalk.
What sort of food do you like as well? Kona is sort of Asian Fusion. Spoodles tends to be Mediterrian and casual. Cape May is a clambake buffet with seafood. Yachtsman is a very nice steakhouse, as is Shulas. Narcoosee's has good seafood. Bongos (in DTD) is Cuban. Whispering Canyon does BBQ. Jiko has an African flair, and Artist's Point tends to have buffalo on the menu.