Zz'rot Portal best utilized on who and how?

The stats it gives are really nice on , as its the only item that gives armor, MR, and health regen without that pesky flat health that soraka must avoid like the plague.

Heimer apparently does really well with it. Not a Heim player so I can't personally testify tho.

Shen would enjoy it, he is THE splitpushing tank after all.

Any big Tank that has Teleport. Sion for example. I mean PURE tank with virtually no need for an offense item.

It is good on and

I enjoy it with Singed. The Point Runner passive alone is great for when you're proxy farming, and using the active (in certain situations) forces the enemy laner to deal with it instead of you or risk losing a lot of turret health.

I also simply build it whenever I'm playing any tank in general, really. Point Runner is strong, the active is stupid strong, and 60 Armor/MR in one item is nothing to sneeze at.

I like putting it on Cho'Gath, myself. It can work on any champion that likes to stack resistances (ex: Taric, Malphite, Galio). It's effective enough on its own (as long as you supplement it with health so you end up with a huge amount of effective health), but its ability to push towers really shows if you take advantage of the way it does more damage as you stack Armor and Magic Resistance.

I sometimes use a Zilean off-build that stacks the Magic Resistance and Armor of Athene's Unholy Grail, Banner of Command, and Zhonya's Hourglass with Zz'Rot Portal (because of the tower damage ratio on every fourth minion). It's a somewhat overly-beefy build for Zilean, but being able to assault both side lanes simultaneously without sending anyone from your team there is a fun and effective strategy. Imagine splitpushing, but never getting caught and never failing to help your team during teamfights— Zz'Rot Portal and Banner of Command let you do that.

Banner is better if you don't want to risk going into the enemy jungle to plant a portal in range of inner and inhibitor towers and for when you don't really want to stack resistances for making your Voidspawn hit harder. Think of it as more offensive in terms of stats and build requirements, but it's less useful for zero-champion splitpushing. Banner minions are cool and all, but they aren't going to take towers on their own. Voidspawn can actually kill towers on their own (without minion assistance) if their health doesn't start decaying before they reach the tower.

Zz'rot Portal itself almost demands a special build to really work well. You need health to go with its resistances, and you'll want to stack more resistances to strengthen every fourth Voidspawn. It's not exclusively a tank item, but it definitely encourages bruisery/tanky builds. The movement speed passive is valuable in its own right— you can plant a Void Gate close to where you expect a fight in order to gain MS for dodging skillshots and chasing/escaping, though your Voidspawn might never reach a tower from where you plant the Gate.

I've seen Nasus use it pretty well. He can splitpush 2 lanes at once with TP or push 1 lane all the way to inhib super fast.