Obviously injuries depend on match-ups, but generally I have found over the years (to my cost) that offensive injuries impact more than defence.
My findings work something along the lines that if you cant score, then your in trouble. On the other hand, if you can score, you can make the other team one dimensional, which helps your depleted defence.
Many a time I have bet a team against an injured defence only to find them score points and put my team in bad situations. I cant tell you how many times this has ended in a interception run back for touchdowns.