You get the best deal for Q&C vouchers at Pepper Market at Coronado Springs, and Beaches and Cream at the Beach Club.
The Vacation Kingdom lunch vouchers work best at Rainforest Cafe at Animal Kingdom, as others have also posted. The vouchers cost $30.50; the surf and turf costs $39.99, so you've already paid for the voucher right there. Add in the appetizer ($8-$9), non-alcoholic drink ($2), and dessert ($6-$7) that you also get with the voucher and you've saved about $26, not including tax and tip which is also included in the voucher. My husband and I usually split a meal here as the portions are a good size.