What dogs breeds tend to be the nicest?

No dog breed is 100% aggression proof or prone. It depends on the breeding, past, and training. Some breeds, however may be more prone to being very protective of their pack and possibly children in it, their group leader etc. There are also breeds who have more energy and will need more excercise and stimulation and will turn destructive if not given enough. You need to find some good books about dog breeds and research which type is best for you. Start with basics. Do you want a large dog or small dog, long coat or short coat etc.