Where are you located as this will determine which oak species would grow best in your environment? Which duck species are you wanting to feed? This will affect their acorn preference.
This
study in Mississippi found that female wood ducks preferred willow oak acorns over water, cherrybark, and Nuttall oak acorns.
This
study in Texas found that Nuttall oak acorns made up 47% of the diet of wood ducks and mallards. Based upon the availability of the various food types, researchers stated that mallards and wood ducks actually preferred deciduous holly seeds and willow oak acorns though. Even though overcup oaks were the most dominant oaks, both species of ducks selected against them and neither species consumed overcup oak acorns.
This
study in Mississippi found that 74% of a wood duck's diet consisted of Nuttall, water, and willow oak acorns while mallard diets mainly consisted of rice and soybeans.