If it is the first day they have shot the field and it is private ground with just a few people and somewhat controlled then go with the modified. If your going to hunt birds that have been shot at before then full or extra full. It helps to know the crowd, if they are a bunch of sky busters and won't let the birds enter the field then better take a full choke, but on most private hunts modified is fine. I take my O/U with improved cyl and full combo and I have both covered. I actually kill most of my doves with Imp. Cyl.