Peke because FNC were losing vs SK and made the comeback turning it into an epic back and forth game, TSM vs CST was CST taking an early lead and not knowing how to close and TSM turtling. CST didn't know how to end and TSM were able to prolong the game for about an hour, not to mention all 4/5 SK were at FNC's nexus about to take it and CST were like 4 vs 2?
The other thing is that peke's situation was one which will likely never happen again- Kassadin against olaf at the nexus 1 vs 1. Olaf is the only champ in the game where no flash is meta (and trynd) and so he can't get to kass who has a 5 second flash. The situation was just unbelievable and I remember feeling giddy after it happened since peke was one auto attack away from gone. Also I think olaf was largely ignored after that game...RlP.
One thing to add is the initiative peke had to do that. He saved his teleport, stayed on 20% health before b'ing, and actually saw an oppportunity which no one watching could have predicted. Any normal person would have panic b'd and defended the nexus. The surprise was what made pekes play iconic, shiptur was doing what he had to do- continue to push, he had no reason to back with his ulti up. Also worth mentioning that peke practically soloe'd the nexus whilst 2-3 CST members had wore down TSM's.
So all in all, we will still call this the peke because well...it was iconic. Shipturs play was epic, but to be iconic it has to be fakers zed play vs ryu or pekes backdoor. To be fair to shiptur though, peke and faker are legends and have both won worlds before, so their plays wiil be more adored.