I would certainly choose free range duck eggs over conventional chicken eggs! They are a little different though. When cooked, the texture is a bit "stiffer". They are great in custards or any kind of baked goods. I use 1/3 duck, 2/3 chicken in frittatas and omlets. Nobody in my family really cares for them straight scrambled. We haven't tried them just fried though.
You're lucky to get them free! We pay $5/doz. Although, when you consider how much bigger than chicken eggs they are, it's like paying $3.50/doz for chicken eggs.
CW-125, part calorie counting, part transition to primal
GW- Goals are no longer weight-related