and kind of silly... but it's like arguing about the #1 college football team, it's hypothetical and prone to be skewed by the keepers prefered pet.
My take:
If I were at the receiving end of a bite from a big king or big indigo... and I got to choose, I'd gladly let the kingsnake bite me over the indigo.
An average adult male indigo will easily consume an average adult kingsnake or milksnake. The picture of the big kingsnake in this thread is cool. That may be near the limit of kingsnake size. You'd have to add 2-3 more feet and about 2 times the weight of that kingsnake to reach near the limit of the biggest indigos, about 9 feet.
We're also comparing the biggest species of kingsnakes against the Eastern Indigo, which isn't the biggest species of Drymarchon. Yellow Tail Cribos (South American Indigos) get to 10 feet.
BUT!....You want pound for pound bada$$, the Mussurana will wrap and eat any kingsnake, milksnake, or drymarchon of equal size. They are probably capable of killing (but not swallowing) either kings or indigos larger than themselves. Clelia are best described as Kingsnakes on PCP. On top of their freakish constriction, they are rear fanged and add a little venom to the mix... although even without the venom they are the toughest.
I keep Mussuranas and Indigos and I've kept several kingsnakes in the past. The order is obvious to me.
I love the topic. Glad we're keeping it real 
Doug T