One thing that's bothering me is, why does Shisui's Sharingan have a unique power when it's not even a Mangekyou Sharingan.
We know Shisui probably didn't have an MS because he would have had to kill Itachi to get it. And while Danzou COULD have made it into an MS after he obtained it(since Kakashi was also able to), we know Shisui's eye had this power while it was still alive because that Hidden Mist ninja said he fought Shusui and he had that power then.
There's a pretty huge difference between Itachi's MS power of "really good Genjutsu" and Kakashi's MS power of "fucking black hole generator!"
I think Kakashi may actually have the most deadly MS power.
I mean, sure, when he was first using it on Diedara, he was very slow and clumsy with it. But since then, we've seen him wink nail projectiles and missiles right out of existence in mid-flight.
You're assuming Kakashi's MS actually GOES someplace. For all we know, it's just destroying what it sucks in.
Realistically, a fight between Sasuke and Kakashi should go:
Sasuke: "I use Amaterasu to set you on fire and now you'll burn to death and there's nothing you can do about it."
Kakashi: "Well, while I'm burning to death, I just crushed your heart into a quantum singularity."
*both die*