I am naming the 5 breeds that I believe are most loyal (weather I have owned them or not does matter just from learning: hearing/reading/seeing &/or owned). Not really in any certain order either:

These 5 I think will be more loyal to one person:
1. Mutts.. of course,
BUT if ya want purebreds then:
1. Akita
2. Chow Chow
3. German Shepherd
4. Rottweiller
5. Boston Terrier


These 5 I think are most loyal to the whole family:
1. Mutts once again,
BUT if you want purebreds then these 5:
1. Great Dane
2. Lab
3. Golden Ret.
4. Rottweiller
5. Border Collie


Boy that was hard to decide as almost any breed can be very loyal, just depends on the individual dog & it's temperment & training & how good of a bond you have with your dog. I would love to add more to each list but thats just an idea.