What sort of dog should you get if you’re looking for a canine running buddy? That depends on so many things, and I’d encourage you to consider not only the running that you want to do, but your whole lifestyle.
Do you have time to groom a dog with a long coat? What about money? Big dogs cost more than smaller dogs. Also, some dogs are smarter than others and need much more mental stimulation. You’ll need to take these dogs to obedience training and give them plenty to do so they don’t get bored. In many ways, these are more important questions than just how far a dog can run.
You need to be able to live with your dog even when you’re not out running.
When you’ve nutted out what you want from your dog, then you can start looking at breeds that meet your requirements. Go to dog shows, and chat to breeders to find out exactly what each breed would be like as a running partner. It can take a little time, but dogs aren’t an impulse buy, and you’ll be much more likely to find a dog that you’ll be happy to share your life with for the next 12 years.