The original, Shawn vs. Undertaker. Fantastic in-ring psychology; fantastic spot; and in my opinion, the greatest debut of all-time with Kane's. A close second would be Cactus Jack vs. Triple H, which has my personal favorite spot in Hell In A Cell history. Followed by that would be Brock vs. Taker.
I always found Taker/Mankind overrated honestly. Slightly because WWE already shown Taker throwing Mankind off the cell to death by the time I actually watched it but only slightly cause it's still cool to watch. But also because their was a lot of downtime in the match and yes it's completely understandable but I'd be lying if I didn't say I was getting impatient after a certain point. Also, post the two spots there really isn't anything too good about it. I thought it was average at best. I guess I need more than two, admittedly awesome spots for me to like I match.
Also, special shout out to Triple H vs. Kevin Nash, which currently holds the prestigious honor of being the only wrestling match to put me to sleep. To bad it was only for five minutes, would've loved to wake up to the next match on the DVD instead of that snoozefest.