Dogs are a long term project, and one of the most expensive ways to protect your chickens, with the longest training time. Get a dog that appeals to you, and work with training, and don't expect much for that first year or two.
Hounds, terriers, and sled dog types tend to be the least likely to succeed at this task, although of course there are exceptions. Guard dogs, working breeds, and retrievers or even pointers are better choices generally. Where you have big xbred coyotes and bears, and stray dogs, large breeds do better, and pairs do well. Then, they must be fenced on your property, managed, trained, all that.
Mary