For a challenge it is definitely deer hunting. While just killing a doe for meat is not that hard, killing a nice buck can be very difficult. There is not a lot of challenge to killing ducks although the conditions now can be a bit tougher than 20 years ago. There are no real trophy ducks to be had. Sure you can mount them and one might be a bit prettier than another but it is hard to tell one greenhead/pintail from another once they are mounted. Which is more fun depends on what you like to do. If you like to pull the trigger and retrieve your game, then you had better bird hunt. If sitting for many hours alone for a single shot is your pleasure, then obviously it is deer hunting. I have done both many times and had fun on most occasions. At one time I spent way more time duck hunting. Now I only hunt deer. When I was younger I loved going into the marsh and setting up. Now, even if I was offered a hunt, I am not sure that I would go. It just doesn't have the appeal that it once did. I have had many more successful duck hunts, killing hundreds of ducks and geese. Maybe I just got burned out on it and it doesn't hold the challenge that it once did. Both are great sports and have appeal for different reasons. My youth was filled with duck hunts and now middle age is filled with deer trips. I think that I have changed from having the need to pull the trigger many times and go out to get the game to enjoying the quiet of the woods and waiting for that one chance at a shot.