Iams is NOT the best
Pedigree IS a step down....
check out
The Dog Food Project - How does your Dog Food Brand compare? , specifically ingredients to avoid for starters...
A lot of shelters, vets, etc recommend things like Iams, Eukanuba, Science Diet, Purina, etc for a couple of reasons. Usually, they really don't know any better. Also, Food reps come out to do 'nutritional trainings' (and endorse their product, of course),
and they make a profit off of them.
I know some here feed Orijen, Taste of the Wild, Natures Variety, etc. If you want to compare the ingredients with the Iams to some of these brands, you can tell a pretty big difference