Short!
I just like Jackson to look neat... and when his hair grows longer, he just starts to look shaggy and scraggly.
I think it all depends on their coat. Some Yorkie's can pull off the long hair and look
beautiful but in general... I prefer short. Plus, we're outside pretty much every day in the warmer months so it's less maintenance for us and he is always so happy after he gets his hair cut!
This is how I like him the best... and it works for us.