I think the 9-11 lbs range is perfect. They are still a very small dog, but a little sturdier than the tinies. Snickers and Baxter are 9 and 12 lbs and I'm thankful they are bigger. They love to roughouse, and I'd be a wreck if I had to worry about them getting hurt or stepped on all the time.
Also, the bigger ones are just so beautiful. Think of all the best qualities of a yorkie, but in a bigger package.