First of all, welcome to YT!
It sounds like you did your homework and have selected two reputable breeders with good quality healthy pups. If you are looking for a show dog, you would be using a different selection process, but since you are looking for a beloved companion who will be your faithful friend for the next 10 - 15+ years, I would visit each breeder's home sit down on the floor and let the pup choose me. Most of the time the REAL beauty of the yorkie lies beyond our sight and within his/her heart ... Good luck!