I can find most game equally tricky depending on certain circumstances. Some seem smart because they're pretty skitish, some are cunning, some can be just brain dead. But in my experience the older the game is, no matter what it is, the harder it is too bag. Look at whitetails, I've had deer keep grazing 20 yards away while I fired my 12ga and reloaded. On the flip side I've also had areas that consistently hold some true monsters that no one ever bags or even sees during season. So are deer easy or tricky? Same goes for pheasants, coyotes, even squirrel.
Killin a sample of most critters can be fairly easy, baggin one that been around the block is another story.