Which of the 133 champs has the best CC?

In terms of reliability....

Currently, these.

The Most or the best(longest)?

Why does no one mention Sion? Sure it's not reliable, but it is a powerful potential 5 man knock up on a basic ability. And there's his ult.

Sion for sure. Although Riven's is certainly strong, especially for her class.

do you mean the strongest CC spell or the strongest CC kit?

strongest CC spell probably E, R or Q

best CC kits definitely

Either Sion or Nautilus

Situationally if you Karthus Ult and get a Penta its the longest CC in the game currently.

for me a tie between and