It depends what you like. Personally, I love C deck between sections 14-30. The sun is in your face on the other side of the stadium, but that's usually only a problem in the early Sept. games. I prefer to have the sun at my back.
Iprefer C deck because, while it's no where near as loud as the lower decks, the view of each play is great. You can talk all day about the closeness of AA and lower A, but you see the plays much better, anywhere on the field, in C deck.
If i'm buying ducats, I'll take C deck any day, unless the A deck were 20 rows up and the same price.
C deck are also cheaper.