I have two border x Lakeland terriers and I feed them Naturediet and plain terrier meal biscuit. No additives or colour. Also they only have treats and chews that are also with no added colours or additives.
Have fed them on this diet for over two years and they do very well on it. I also give them both one flaxseed oil capsule daily.
I have a small active breed and they are fed on Eukanuba Adult Small Breed. Nice firm poos, and shiny coats. My oldest is almost seventeen and she has been on it all her life.