Infinite Fight: Rammus(33%), Sion(25%), Shen(20%), Amumu(12.5%?+1.5%), Gragas(14%*), Alistar(13%), Taric(10-20%), Singed(10%*), Blitzcrank(6.25%?), Malphite(1.5%), Galio(1.5%)
10s: Rammus(40%), Sion(40%), Amumu(20%?+20%), Alistar(20%), Galio(20%), Gragas(20%*), Shen(20%), Malphite(15%), Taric(10-20%), Blitzcrank(10%?), Singed(10%*)
5s: Rammus(60%), Amumu(20%?+40%), Alistar(40%), Galio(40%), Shen(40%), Sion(40%), Malphite(30%), Taric(20-40%), Blitzcrank(20%?), Gragas(20%*), Singed(20%*)
The above is a ranking--and calculation--of the percentage of time a champ can maintain crowd control on a minimum of one enemy for a given length of time. Actual toughness is not used in these rankings--but all do have the "tank" tag--.
The first section is representative of an infinite fight; there, champions whose CC is in an ultimate with a long cooldown to very poorly while those with quick cooldown crowd controls shine. An infinite fight is not very realistic of the average fight between champs/teams; it may shed some light on laning, but really it just establishes a high end of the study.
The second section is representative of a ten second battle. This can be representative of a fight where the combatants do not fully commit to an all out fight and are just flee-ing/rushing back and forth; it can also represent a long battle--should one occur--.
The third section is representative of a five second fight, a decisive and committed fight to the death.
Method:
The formulation for the infinite fights were: stun length / cooldown. The formulation for the 10s and 5s were (initial stun length + possible second stun length) / the respective combat length.
All data presumes optimal timing--in that skills are used immediatly after the cooldown--. For the purposes of this comparison, crowd control includes stun, taunt, and reverse-movement. It is understood that a CC may be used to better effect when aimed at someone charging/using an ult; in most cases this would drop the percentage of time the enemy would be stunned.
-Stun cancels enemy attack and movement potential while rooting them in place. (Damage Negation + Stopping Power)
-Taunt forces the enemy to normal attack and follow. (Damage Redirection + Movement Control)
-Reverse-Movement includes any ability that can move the opponent in a skill-user designated area. Both Graga's and Singed's crowd control are reliant on this type. Since R-M does not negate or redirect enemy damage, this type of crowd control is not always useful in a fight.--It does still have many uses in fights however--.(Repositioning)
In searching for the specifics of the involved champions and thier respected skills, both leagueoflegends.wikia and leaguecraft were used. Of the 11 tanks with the above specified crowd controls, Amumu's and Blitzcrank's stuns do not have a listed stun duration; a 1s duratation was used in the calculations--it may well be longer but it is unknown at the time of this writing.
It should be noted that both Amumu's and Galio's ultimate-crowd-control are AoE and therefore can affect muliple opponents.