Actually, Kaltenstein is the largest, toughest (Body 35), and strongest (Strength 60).
Lofwyr is the second biggest physical badass, then Ghostwalker, and finally everyone else. At least among those assembled Great Dragons from the Rite of Succession council during Survival of the Fittest.
When I said most poweful overall, I mean that in a general sense. (Which you may have caught, I'm not certain, but I'm clarifying anyway).

He's powerful magically and phsyically, even if not the top dog in either field. But he's also got sole control of a megacorp, something no other dragon can match. And for all the wealth, knowledge, and power the other dragons have, a fraggin' Corp trumps them all, especially when added to his already considerable talents and assets.
Ghostwalkers still my favorite great dragon though (Well, living one, anyway). I just like his moxie and attitude. Lofwyr has the ruthless corper thing down, but in the long run, he's sold out to become "the man". Ghostwalker though, he's not afraid of anyone's drek, and he's willing to back his words up with action.

Sirrug is also fun.