I also want to remind you guys that a good TF can stun every 3-4 seconds for 1 sec. Nobody gets away from that.

My top 10:
1. Sion/Taric/Annie/Ashe - Raw, long stuns. Best there is, no questions asked..
2. Malzahar/Warwick - Suppression. No casting and no motion. Gotta love it.
3. Cho/LeBlanc/Kassadin/Garren - Silences. Next best thing to a stun/suppress, IMO. Stops them from casting.
4. Rammus/Shen - Taunt. Can't cast, and you can walk them to where they belong. GG.
5. Poppy/Alistar/Gragas/Tristana - Knockbacks kick ass. They pull people away from the scrum, interrupt and can separate people for a good beating.
6. Swain/Veiger - Delayed stun. Limited use, but very effective if they land.
7. Morgana/Lux/Ryze - Snares are BA, but lower on the totem. people can still do what they want, they're just stuck in place.
8. Janna/Cho/Blitz/Maokai/Malph/Xin - Knock-ups are cool and all, but they only interrupt, and only have a flash of disable.
9. Leblanc/Kennen/Panth/Maokai/Etc - Situational stuns. They're good when you need a quick escape route, but are markedly less effective than hard CC.
10. Slows. All slows. Great CC when paired with any of the others, but on the whole aren't exceptionally useful.

My choices for best:
Sion, Taric, Rammus, Gragas, Lux, Annie, Ashe, Cho, Veiger, Garren

fiddle fear has a similar range to sion's stun, and it's insta travel, and lasts 3 seconds.. and fear is just a good as a stun, since they can't atack or do ****.. i would put it top 5

How can someone ever prefer silence over fear?.. that's just quite dumb

Tempest is definitely number 1, his ultimate goes through all magic/physical immunities and can disable a team for 5 seconds for an easy genocide, need a portal key to get a good intiation off. Treant is also pretty good with a refresher giving you 10 seconds of immobilise.

In my opinion, Blitzcrank is the number one CC player in the game. If you're good with a blitzcrank no one can escape from you. I stack CDR to max on him so my grabs are up every 5 secs or so and my power fist is up every 2-3 seconds. With max CDR his overdrive is only on cooldown for a second after it stops, and his ulti is up every 19 seconds. So lets see, overdrive into a fight, silence everyone, power fist one person into the air run back and grab before they land, power fist again, chase with overdrive, power fist when its back up, grab, and rinse and repeat. Not to mention the ability to pull near towers and bait with flash. Throw a rylais or a frozen mallet and the slows prevent anyone from even advancing towards their base. GG.

In my opinion, taking into consideration costs, cooldowns, and all levels of the ability:
1: Amumu's Ultimate
2: Galio's Ultimate (Both these 2 champions are picked basically because of their ults.)
3. Blitzcrank's fist (Easiest way to turn a 5v5 into a 4v5 before it even starts.)
4. Sion's Cryptic Gaze. (A 2 second stun at lvl 1? Yes please.)
5. Fiddle's Terror
6. Rammus' Taunt
7. Shen's Dash/taunt
8. Veigar's AoE stun
9. Singed's Toss
10. Malzahar's Ult