The original CSI was fine throughout the Grissom run, and gets points for William Petersen, who is much more animated than the ever-earnest, almost righteous Gary Sinise.
That being said, my favorite single season was CSI NY, season 1. The sets and the atmosphere had a much darker tone than either the Vegas or the subsequent seasons of NY. Although the latter were good, the tone was brightened up, so the look inched closer to Vegas, hence less differentiation between the two locales, except you would find bodies inside Macy's instead of Bellagio. As it wore on, the NY series did seem to be pushing the envelope of obscure facts used to solve crimes, as in "Only two shops in all of New York carry live Sudanese Tsetse flies, but one of them is closed on Wednesdays, so we know it couldn't be that one, since our perp's day off is Wednesday, and that is likely the day he would purchase them".
Miami? That means David Caruso. Forget it. Yeaaaahhhh!