Truth is there are countless stereo-types given to each gender. My opinion is simple: all Cavalier King Charles Spaniels are smart and can be taught right from wrong. Potty training and marking are two very different training issues and seems to be the biggest concern inquiries have regarding males. Truth is both genders are capable of marking. Males tend to mark if they come into contact with a female in season once they are old enough to sire a litter which is around 12 months of age. I recommend companion pets to be spayed/neutered at 12 months of age.
Females mark for odd reasons and can be more difficult to correct. A female might mark when being left alone or to show dominance over another pet. In the dog world females are always alpha and above a male in the pecking order. Males establish their pecking order against just males and do not tend to mark when being left alone or to show dominance...they just mark when a girl is around who is season. To get around this issue with a female who is maring it is best to always crate train when you are gone so you will know your Cavalier King Charles Spaniel (dog) is safe from developing a bad habit of marking.
There is a saying amongst Cavalier King Charles Spaniel breeders and it goes like this: "Females love you, but males are in love with you." Every Cavalier King Charles Spaniel is different as to how it goes about showing its affection for its owner. I have had some males and females that are born snugglers and I have others that are more sporty and would love for you to throw their toy so they can retrieve it. As Cavalier King Charles Spaniels mature in age I have found the males stay a bit more outgoing towards other people and activities outside the home, while females tend to get a bit more home-bound and tend to create a comfort zone of showing their affection only to their family members. I have found males tend to blend better with children and are more likely to play with children while females tend to locate the woman/mother of their family and she becomes their significant other...or they will gravitate to the one who sits in the chair the most. Both genders are active as puppies through 12 months of age, but once they reach 12 months you will notice a more relaxed companion...girls especially will begin to become less active while boys will continue to interact with the children in the home...therefore, I highly recommend a male if a family is looking for a dog who will interact with the children more as they continue to mature.
I recommend to anyone looking to adopt a Cavalier King Charles Spaniel to focus on temperament and not to let gender be your main priority because you might miss out on a remarkable relationship if the other gender had a temperament that met your lifestyle better.