Crossbows are the easiest to aim well, they can be used with optical sights like a firearm. There is no effort to hold the string.
Compound bows would be second on the list. They can have sights, the pull wieght is reduced with let off so you can hold the string with less effort.
Last would be a traditional bow, usually no sights and you hold the full draw weight. However they are very light weight and simple in design. Not much can go wrong.