I know you can purchase Blue Buffalo at Petco, but I'm wary after them about reading about some things. See the thread below for more info:
http://www.yorkietalk.com/forums/yor...-formulas.html From a link in that thread: "...revealed cases of hypercalcemia secondary to vitamin D toxicosis occurring in dogs that eat a single brand of dry pet food: Blue Buffalo Wilderness Diet, chicken flavor."
I was going to buy BB until I did some research. I know a lot of pups do well on it though! It just wasn't for me. Every pup is different with different foods. I've been told it is trial and error.
The first food I am trying is Natural Balance L.I.D. Small Breed Bites.
Good luck in your food search. Out of the two you listed I would go with Acana, but that's just me.