I'm often asked about the differences between males and females... these are my thoughts.
Note: This is very 'generalized' - the Papillon breed is very friendly and outgoing, loyal and loving. I love all my dogs and everyone of them is wonderful.
If the Papillon is 'in-tact' ... BOTH males and females in their natural state will mark. Males tend to mark more often and have a much stronger odor, however they are easier to block off by using a belly band (a 2" strip of material with 1/2 a disposable kotex placed against the penis) to catch the drips and easily dispose of it. Females can use 'panties' but they are a bit more cumbersome. Both males and females will 'hump' on occasion, with some doing much more often - this is usually curbed with neuter/spay and a sharp no when witnessed (I also use the sign language 'no' so the puppy/dog can see 'no' in addition to hearing 'no'.) Males will occasionally have their penis out which can be embarrassing to some people. I love the look of the fluffy chest hair (lion-ish) and very narrow waist of the unaltered male - so regal and commanding.
If the Papillon is neutered/spayed...
Female dogs are called b****** for a reason. They are moody. They love to be adored and want to be petted continuously. If you stop petting them, they'll nudge you asking for more or you'll get 'the look'. If you still do not give them the attention they seek, they will often move to a location where they will sulk, occasionally looking at you to make sure you know that they are sulking.
They will sometimes be like a cat... I want you to pet me when I want it and not when I don't. They are friendly, fun, sometimes prissy while other times frolicking or rough-housing.
One Papillon owner summed it up perfectly by saying...
"The female lives to be loved and by you, whereas the male lives to love you."
Males tend to be a bit more 'needy'. They will often be more aggressive sounding if someone comes to the door and may be more reserved/guarded with strangers (this shows more as they get older). They are extremely loyal and are often a shadow wanting to spend every moment with you. When you get tired of petting the male, he will also 'ask' for more attention, but then will lie beside you (or mine like to lay their head on my foot) and look at you adoringly. They are friendly, fun, silly, loyal and love to play, but above all be with you always. When neutered very young, the male will often have body look of the female - still beautiful, but missing that little bit of 'lion' look.
These articles are written by various authors giving helpful advice regarding different areas of your dog's life.