User blog comment:LionsLight/Sunfire Cape/@comment-4073002-20120107204712/@comment-4568240-20120108143138

Frozen Heart is probably the single best item in the game for reducing melee damage, both for yourself and for your team, considering the 99 armor and the attack speed debuff that's automagically applied, without them having to focus the tank or be in the wrong place to get tagged by it, like with Randuin's. The huge chunk of mana and cdr is also hugely beneficial, particularly to cc-dependant tanks like Alistar, Leona, Singed, and Maokai. Randuin's is cool, too, but it's kind of a late-game item, do to the high cost and dependance on already built-up armor and mr to be super-effective. Sunfire cape does relatively little to help you out with melee damage, since it doesn't really have much more defense than it's component parts. Better off with turning that giant's into a FMallet, Warmog's, or Rylai's, for the slow, survivability, and slow, respectiely, whereas that chain vest is more useful as a glacial shroud, warden's mail, or GA.

Now, Sunfire cape is certainly not the worst item in the game, and I'm sure there are some situations where it might be a good choice, Rammus and Leona maybe being champs I'd consider it on, due to the fact that they tend to stick to worthwhile targets and can get good use out of it, but it's an item really held back by lackluster stats. It's damage is certainly noticeable, particularly in a prolonged engagement, but it's really more of a situational item for brawlers than a semi-staple for tanks, in my opinion.