Thanos (Planeteer), Doom (Super Doom), Mephisto (LOTR)

  
Thanos has Earth, Fire, Wind, Water and Heart rings 
 
Dr. Doom has all 7 Chaos Emeralds 
 
Mephisto has all the Rings of LOTR and the One Ring that rules them all 
  
Data has 5 power Rings (His Emotion is on)
  
Popeye has the MASK 
 


 
 
Take the guys above and rate them in power here: 
 
  

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2. .
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5. .

1. .

I want to say Doom, since those emeralds can supposedly really amp characters up. 
Thanos summons Captain Planet and proceeds to vaporize him, along with the rings, with a casual blast.

I'm going with Doom with the chaos emeralds. Going by the 3d games, the only being who ever even harmed a Super hedgehog was Solaris and he was so powerful he was screwing up all of time itself. Even though it was only in gameplay, there's never been another boss in a Sonic game that's ever been able to harm a Super hedgehog at all.
I think in the archie comic series, the chaos emeralds have infinite power. In the comics, the floating island was formed by using chaos emeralds to lift up the city the echidnas lived in to save themselves from a giant meteor heading towards them. Eventually, they tried to find a way to unite back with the planet and devised a plan to syphon off their power but all that did was result in all the chaos emeralds save one to be absorbed into Dimitri turning him into Enerjak. Despite only one chaos emerald remaining, the island stayed afloat and they said it must be because it has infinite power. And that same emerald kept it floating for hundreds of years.