The friendliest small pets suitable for adoption include guinea pigs, rabbits, hamsters, rats, gerbils, and sugar gliders. These animals are known for their social nature and ability to bond with their owners. Betta fish and parakeets can also be friendly and interactive pets, particularly with proper socialization and care. When considering adoption, it's essential to research each species' specific needs and characteristics to ensure they align with your lifestyle and preferences. Consulting with a veterinarian or experienced pet owner can provide valuable insights into selecting the right small pet for your household.