Well I still can't regard an accidental achievement as evidence of being powerful, but that's not really something that we can argue about.
Also, I count gaining power by politics as a significantly greater achievement than taking power by force, because it takes true genius to be a politician and eliminate an entire government bloodlessly. To win power by force it takes merely the courage to pull a trigger. As far as I'm concerned, the pen is mightier than the sword and no one could wield either one of them like Darth Sidious.
As far as Krayt vs. Sidious: The Republic itself was far more stable when Sidious destroyed it. In fact, it had been operating continuously for 25,000 years. Not even Revan could destroy it. Besides, not only did Krayt basically inherit everything from Palpatine, but he never really established true peaceful rule over the galaxy and, as you mentioned, ruled for less than half the number of years. But I don't think you were ever really arguing for Krayt anyway.
Yeah we keep getting hung up on EU stuff. Like I said before, I'd really like to believe in the Chosen One. For now, I guess we can agree on the fact that even if Anakin Skywalker didn't destroy the Dark Side, he still had more potential than any individual ever had and ever will have.