I have to say season 7. Not only was there so much GunShotResidue (Which just annoys me because such a supervisor/subordinate relationship is something I've always found to be wrong, irresponsible, and just plain unprofessional...), but also because I *every* other season I actually had an episode that I could call my favorite.
I can also list numerous episodes from every past season- except I just couldn't care less what episodes were called this season.
But, in season one, I liked too many episodes to just consider any single one my favorite. Season two, had episodes such as Stalker, Overload, and Organ Grinder.
Season three had episodes such as High and Low, Fight Night, and Lafy Heather's Box (which makes the above comments about very few memorable moments from that episode really hard to agree with, because a) Lady heather isn't easy to forget (even moreso now that she's been back in other seasons...) b) it was also the season where the lab exploded, injuring Greg (Play with Fire) and c) It brought a close to Catherine's marriage by the death of her husband- something they'd been putting in numerous episodes throughout the series before Lady Heather's Box. (which is leaving out all the Nick scenes that I still think are awesome...) As for Season for, I enjoyed the whole promotion and how that played out between Nick and Sara. I especially liked the first two episodes of the season with the serial killers who went after other married couples.
Season five had Grave Danger- and that was more than enough to make it my favorite. But even without that episode, I still enjoyed many of the episodes, despite the split in the shift. Season six would have had my vote, but with a few episodes such as Gum Drops, and The Unusual Suspect it beat out season seven pretty easily for me.
Frankly, there aren't many things that I *want* to remember about this last season. Spending half of it on a single serial killer case was just too much for me- especially since it isn't even over. And the way they just sprung out this Natalie character in the last episode was lame. There was absolutely no buildup to the first showing of the character, and it just seemed so random. Perhaps if they had shown her cleaning around the lab earlier, or if they had shown a picture of her when looking through the foster kids it would have been far better. Then add in the GSR, and I just got annoyed by many of the episodes. A few scenes here and there throughout the season helped lighten the blow *very little but still a bit*. Overall, The entire season was simply about Greg's attack in the alley, the Miniature Killer, and GSR. All of which got old really fast for me. I also can't remember seeing a single detective aside from Brass and Sofia, and that just annoys me because I really enjoyed Vega, Vartann, and Cavaliere in the past seasons. It just focused on three characters really, and in a show with such a big cast, I'd have liked the time to be spread far more fairly and evenly.