Ok, here's what I think about this. When I had to get a livestock guardian, I spent a lot of time researching online and talking to local people.
I was told by more than a few that donkeys and llamas can make great livestock guardians but ONLY if they like the animals they're protecting. If they don't like their "charges", they will not only not protect them, but they may hurt them.
I was also told by more than a few that the donkeys sometimes got aggressive with their owners. So that when the owers would go to do stufff with their charges, the donkeys would come after them. But I'm sure that's a potential problem with any livestock guardian.
That said, I chose a Great Pyranese
she's worth her weight in gold and I'm very pleased with her.
That's not to say that donkeys and llamas aren't good livestock guardians, because they ARE. But you need to get one that will be a good fit with the animals you are trying to protect.
However, I think I should also mention that one donkey, one llama or one LGD is no match for a pack of dogs or coyotes. You will need more than one, whatever you choose, if you have multiple predators. I still like the great pyranese because they work very well as a pair and it's one of their traits: one patrols, one watches. This is what makes them effective when predators like coyotes work together to leur dogs away from home, or livestock guardians away from their charges.
Er, I'm also editing to add: When I spoke to neighbors, the consensus was to get full sized donkeys, not miniature, because those I spoke to lost a few of the mini's to coyotes and dogs.