^^ That and other things/reasons was why I felt the series should've ended after the Cell Games, even though most think it should've ended after the Frieza Saga. The stuff that happened after Namek was one of my favorite arcs too. Not just because of Cell, but the Androids as well, Piccolo's newfound awesomeness from merging with Kami, and I guess Hercule also to some degree. But the Buu sagas had about as much over-the-top ridiculous stuff as GT itself.
Those pics are from the DB Universe webcomic, right? I just discovered the thing.
Zack, when you say Cell at his best, you mean after he comes blows himself up and powers up, right? Not "Perfect Cell" as he fought Goku, who was a good deal weaker?
If that's who it is, I'm giving him the nod, partly because he gained Goku's teleport trick. Teleport > stone spit as a cheap power, as Goku proved time and time again. (For one thing, it let Goku 'port right next to Cell with his fully charged Kame, making dodging impossible, and it let him get the drop on Kid Buu)