well, i can see S7 being the "Sara" of the seasons - the one that wins as both - the favorite and least favorite. the last season definitely was the one you either hate or love b/c it was so distinctive and a bit different than the others. it triggered opposite emotions in the audience. personally i loved it, and as many critics say, it's been one of the strongest seasons CSI had, if not the best one.
on the other hand, S6 deserves the crown of the weakest one considering how much money they had and how, well, boring it has been. except a couple of episodes like Still Life, Secrets and Flies, Gum Drops, Rashomama, Shooting Stars, ABRTI's, The Unusual Suspect, POTTR and the final two parter (i rewatched it recently and actually realized i liked it a lot). so i'd say they had only about 11 good episodes out of 24. while in season 7 they had 24/24.
i'm really glad that CSI competes with Grey's, b/c the competition always makes the consumers better off. i have a better show to watch, and that's all that matters to me.