We LOVE our Kongs. Winston has the black one, we have a puppy one from puppy days, and Harley has a small red one.
Sometimes I stuff it with a dry treat; sometimes frozen peanut butter, yogurt, pumpkin, cottage cheese, etc. They usually get a stuffed one when left for the day to keep them busy and eat it before it makes a mess. Freezing it helps, too.
When I'm lazy, I'll just scoop peanut butter on a treat and squish it down in there.