Male and female dogs can both be trained effectively, but female dogs are often considered slightly easier to train due to their higher focus and lower distractibility.
There is no definitive evidence that one gender of dog is more loyal than the other; loyalty depends more on breed, upbringing, and individual personality.
Affection levels in dogs depend more on individual personality and upbringing than gender, though some owners perceive females as more nurturing and males as more openly demonstrative.