Boy or Girl Puppy ?
I think gender differences become unimportant when Yorkies are
spayed or neutered.
I have raised, trained and loved both female and male Yorkies. Behavior is more a personality thing, than a gender thing.
Right now I have five Yorkies. They are all different.
My boys are more affectionate and less barky than the girls. They are less demanding about being right next to me, or being first for treats and so on. They do love being groomed and petted. The boys really don’t care about being the top dog and let the girls boss them. They were not any harder to potty train.
Abba Daddy is the sweetest most gentle Yorkie I have ever had. He is small around 4 pounds of love and is never in a bad mood. He enjoys being brushed, and napping with me. He puts up with bows, little shirts and neck kerchiefs. Abba prances around after his bath like, look at pretty me. Abba Daddy is a therapy dog. And our little stud.
Rubin come from a long line of show dogs. He does not have a good bite or the right coat to be a show dog. He is our beloved neutered grand puba. He is ten years old and kind of set in his ways. He prefers people play, to doggie interaction. For the most part Rubin is tolerant of the other dogs and has only had one fight in all these years. He also smiles a real toothy grin. He is 100 % a Mama's boy.
My girls are Gracie Poo, Ginny Joy and Julia Rose. Gracie Poo was a rescue and came with many personality hang ups. She was fearful, yippy and terrible about guarding. It took a really long time to even brush her without getting bitten. Gracie became the Yorkie pack boss, she only defers to me. Gracie nips the other dogs if they bother her. She is a little, selfish, diva. Gracie has a 'had a bad start but, look at me now' attitude'. Gracie is all ‘what about me ?‘ we cherish her anyway. Of course Gracie is spayed. No way would we risk breeding her, we have no idea what her Puppy Mill / pet store genes would be like !
We got Ginny Joy as a puppy. She was from my own Noah’s line. (RIP Noah ) Ginny Joy is very sweet, not a licker, and she does love to snuggle. She is very smart too, as a puppy she learned how open her crate and the other Yorkies too. Ginny would make a perfect only Yorkie, like Rubin she is more into her people than her canine family.
Julia Rose is a real brat she is still in puppy mode though. Bouncy happy, playful and way too barky. (she is still learning) She is very smart and keeps us quite busy.
So to answer the original question, look for personality, spay or neuter after sexual maturity* and don't worry about picking a boy or a girl. Love makes the perfect match.
* I have read a lot lately about waiting to
spay and neuter until a dog is sexually mature. Several studies conclude it is better for bones, teeth, organs and personality development. My Vet has convinced me it is a real advantage to wait until Yorkies are at least 1 year of age.