The types of donkeys are labeled by their sizes; 36" and under, Miniature Mediterranean, 36.01-48", Standard, 48.01" to 54" (jennets) or 56"; (jacks), Large Standard, and 54/56" and over, Mammoth Stock. There are no real populations of BREEDS of donkeys left, such as the Catalonian, Majorcan, or Andalusian. http://www.lovelongears.com/about_donkeys2.htm
Donkeys are a herd animal, they need to be with other donkeys or other animals. The leader protects the herd from their natural enemy the wolf, or canine. That is why they will sometimes be used as herd protectors for sheep and goats. There are special ways to get a donkey prepared for this type of work. They are also all terrain animals but will not go anywhere they consider unsafe.
Donkey require low protien hay, a salt block, mineral block and access to fresh water. Having evolved from the desert, their digestive system works efficiently extracting 99% of the nutrients over a 48 hour period. Sugar and high protien are bad for donkeys. Giving love on a regular basis instead of treats is much better in the long run.
Donkeys are not maintenence free. They need a shelter and fresh water, they need to have their hooves trimmed regularly. Older donkeys need their teeth floated. They should be groomed and also taught to stand for medical care when needed. Parasite control is very important.
This is one of the reasons why donkeys are called stubborn. Donkeys will stop and assess a situation. Donkeys make a choice to move forward, leave, or attack. Donkeys have excellent memories. Some claim donkeys can remember places and friends they haven't seen for 25 years.
Donkey can be trained to do the same thing a horse can, but unlike a horse they cannot be scared into doing something. They need to learn what you are asking them to do. They get bored easily and prefer a variety of training tasks. Always, always, always leave on a good note.