I live in a large apple producing area in Western NC. Many orchards have 12 or more varieties. I deer hunt in the eastern part of NC where there are no apple orchards. Every October I buy a few bushels of second quality apples to put near some deer stands. Some years they eat them and some years they don’t. Might have more to do with acorn mast than the apples. They last longer than corn because squirrels and turkey don’t eat them.

What variety of apples do deer prefer most? Do they prefer sweet, tart, red, or green, etc?

Not sure what there preference is, but the "wild" apples on my place were various colors, ripening times and all were tart....they ate them all....

here they eat any and all apples

I can't believe squirrels and turkey's will pass up an apple for ANYTHING else.

All apples , pears and any other fruits are eaten quickly as they fall or what can be reached from their standing height. The higher ones need to be frosted a couple of times before they fall, then they are gone quickly.

Golden delicious is the best I've found for deer.

Deer were hitting the yellow and red apples at the ranch until bears ran them off then coyotes started eating them.
Spouse watched 4 coyotes raiding the orchard until we got the rifle out.

rather than buying seconds or utilities , ask if you can pick up ground falls , at worst they can say no , but if they know they are for deer, they might say 5 bucks a bushel or free.

Hunted in Pa years ago. Apples everywhere. The ones the deer preferred were the ones that if bitten would make the glans in your neck explode.