The title says it all. They are obtained by trading their prevo's with each other; an evolution not seen before these two. One begins with the appearance of a ninja, but evolves into a knight. The other does the opposite, first appearing as a knight, whilst evolving into a ninja. They both have a base stat of 495, and are of the Bug type (Escavalier being Bug/Steel, while Accelgor is pure Bug).
Who do you prefer?
Who would win in a battle?
Who has the better design?
Who is more valuable?
Personally, I must go with Escavalier. In fact, it's my favorite Generation V Pokemon. Possibly, my all time favorite.