depends what you like.
if you like to be closer to the action, and are willing to sacrifice your view of certain sections of the field A deck is for you.
if you like to see plays develop, and willing to sacrifice and be a little further from the field C deck is probably your cup of tea.
Personally I like C deck, and have season tickets on the 50, on the visitor side. I have requested the same seats for the past 4 years and i really like them.
The downside to visitor side, and maybe specifically C deck, is that the sun will be in your face late afternoon, however for USC game this won't be an issue.