I have both a shih tzu and a yorkie. I honestly can say that it takes me 1/10th of the time to groom my yorkie as it takes to groom my shih tzu! I bathe both of them once a week, and brush both of them daily. Belle's coat has never even had a tangle, it takes less than five minutes to brush her. Oliver, on the other hand, always has mats starting to form in his coat and it takes at least half an hour to brush him thoroughly when he's been clipped for the summer - and MUCH longer when his coat is long!
They both bark a little, but neither one is yappy. They just bark at the cats or at each other when they are playing. Belle also barks to tell me that she's happy I'm home and that I should pick her up and give her some loving.
Oliver is my first experience owning a shih tzu (he's actually the first one I've ever known) and he's a real sweetie. I love him dearly! He was a gift from my fiance who thought that when I said I wanted a yorkie that I just wanted a small dog. (His breeder is a friend of ours)
I grew up with Yorkies and they are like no other dog - I finally got my Belle in February and now my family is complete
Good luck with your decision!