Obviously the more expensive the better however some lower market brands are just as good.
My dog has a 15kg bag of supadog sensitive at 24.00 a bag.
however the normal supadog adult is around 15.00
never had any problems with this food
Eukanuba are also rather good as i recently went to a training evening hosted by them and found some of their facts very interesting.
Especially in the breed specific range.