One of each
I got Loki first and he is my boy. We did training together and I know exactly what he is thinking. We have a special bond. Last night we were watching Modern Family and they had smoke detectors chirping (he HATES that) and the first time I heard it, he was sleeping on the loveseat and he was on the couch. He looked up at me, bug-eyed (scared), I held out my arms, he jumped into them and slept on my lap the rest of the show.
Sammy is awesome, but she is crazy and she doesn't usually *need* me. She loves my husband because he plays more with her and he plays rough with her, which she loves. She is a happy dog, loves meeting new people and goes shopping with me but is a cuddle bug only when she wants to be. She's fun to dress up and take places, and we laugh at her constantly and absolutely adore her, but when I come home, I want my Loki and he wants me. When Sam wants to snuggle though, watch out, because you better snuggle
I realize every dog's personality is unique, but these differences are ones that I've heard before and not just with Yorkies. Girls are divas, aloof, they do what they want. Boys want to please you, be with you and need you.
Either way, you will want the other, and I love everything about my dogs very different personalities, for different reasons.
There are PLENTY of adorable clothes for boys, so if that is your hangup, don't worry about it. If it's a situation like you are out-numbered by sons and a husband, and you want your girl, then get a girl
But if you just arbitrarily want a girl, then eh, consider a boy!