Let's see who gets this answer right first.
EDIT:
And the winner is....Meta Awesome.
Pillar = Knock Up, Slow, Impassable Terrain
Or maybe
's Gravy Field = Slow, Knock down, Stun, Center Drag
7ha7guy7772 votesSion ult? You can cc yourself and up to 5 enemy champions every 36 seconds with 40% cdr
Predatore1 votesnautilus? misread, let me think again no idea... cho q?
Aldirion3 votesBards R -> You can CC ANYTHING and ANYBODY!
A Teamfight around Baron? -> You can CC all 10 players AND Baron for 2.5 seconds if you place it right ;) (well actually that would have been casting it wrong ^^)
nananananacat1 votesNasus Wither?
nananananacat1 votesMalzhar/WW suppression?
BattleOxe1 votesGnar?
TacoKing1 votesAshe Ult.
4ManVotedAgainst1 votes
CreationFlaw1 votesAlistair Q? Knockup + 1 second stun?
Or Akali Shroud, 8 seconds of slow.
Scribbs1 votesMorg ult.
JoeDerp1 votesMorgana snare. Actually get afk warnings because of that shit.
Angry Monster1 votesLee's ult a targeted knock back that knocks up others over 10 temmos.
Decrit1 votesA random skill of Riven.
She makes the enemy player go afk to flame or to despair usually.
orla211 votesBlitz pull under his turret
Samflash31 votesWhoa I thought someone would have figured it out by now. It's not any of the answers listed so far.
SEKAI1 votesI am shocked to see no mention of 
's disgusting CC station ultimate, like how?
EDIT: Ah I am so glad to be wrong, there is 1 mention! Thank god I am not alone here. EDIT2: Someone said Bard's R and they would most likely be correct. I just tend to ignore the CCs that work both ways as it's too unreliable.
LaceUp231 votesWhatever you're thinking, the answer is obviously Bard. He can stun all 10 players at one time.
MetaAwesome1 votes Pillar = Knock Up, Slow, Impassable Terrain
Or maybe 's Gravy Field = Slow, Knock down, Stun, Center Drag
Samflash31 votesAnd the winner is....Meta Awesome.
IcyPepper1 votes
?
?
darapier171 votesstifle 3-sec silence and buff removal
irelia's passive-up to 40% tenacity
lissandra ult-zhonya's/stun for 2.5 seconds + 40% slow
Orbv1 votes
--> R
Death is the best CC