I would argue that yes, Sweet Chin Music is the best finisher in WWE history. Between its effectiveness, it being able to come from anywhere and from out of nowhere, and how many memorable Sweet Chin Music's we've all seen, it's the best.
As for Triple H-Shawn Michaels HIAC, I watched it recently and thought it was an epic. I understand what they were going for with the drawn out ending, but I did think that was a bit much. Other than that, it was overall one of the best HIAC matches ever. If I had to put which ones I think were on par with or might've been better, I'd put HBK-Taker, HHH-Cactus Jack, Taker-Lesnar, Batista-HHH and Edge-Taker. So it's definitely in the top 5 or 6 Cell matches ever.