I would choose Product A, for the same reasons as I choose my own foods:
1) First ingredient is lamb. I love lamb, so should the puppydog.
2) It is specific in its list of ingredients, whereas for Product B you don't know what cereals and bran or where the vege protein comes from.
Unless A is 4 times more expensivce than B or I have a high energy dog, in which case I would choose B or look for another product.