A lot of discussion on foods has taken place in these 2 threads on YT, but be sure to do your own research!
I also highly recommend the book Yorkshire Terriers for Dummies!
http://www.yorkietalk.com/forums/yor...-you-feed.html
http://www.yorkietalk.com/forums/yorkie-health-diet/213019-preference-between-blue-buffalo-formulas.html
Hope this helps and good luck in your search!