I LOVE NB. You can see I have been singing its praises on many many threads now
I would go with the NB because it is grain free, but that is just me. That is why I went with it for my cat, Suki, who has food allergies. She cannot have grains.
It all depends on what your pup is allergic to though. If you want the higher protein you could always try the Go! and if they are still itching go to the NB for the grain free to see if that works.
I personally love NB. I feed the LID to both my cat and my pup (Rylie). Rylie does not have allergies, but I feed her the NB potato and duck anyway. It is a high quality food and I have to make sure Suki would be okay if she got into it.
In addition, I am against a high protein diet for Yorkies due to the fact my Yorkshire Terriers for Dummies book said that the protein content should not be too high. Now I know many members here disagree with that and their pups seem to do great on higher protein diets, but I personally did not feel comfortable going against those protein guidelines after reading from multiple sources that I shouldn't.
It is up to each individual though! I say as long as your pup is healthy and does well on it, then it is a good food.
