First off, metal/bug type is great! Only one weakness, fire, and a whole bunch of resistances (9, to be exact, plus one immunity). Bug types have three weaknesses and three resistances.
Also, Escavalier may have a high attack base stat, but he also has very high defense and special defense stats (105 each). Accelgor may have speed, and a decent special attack, but it very vulnerable with its weak defense.
Now, let's look at the designs. I will base them off the BW sprites:
Accelgor just lacks concept clarity; I don't get ninja at all from the sprite. It looks like it is a straight-jacket without legs, and then a red/green snail shell on its head, that has what appears to be a black crack the front of the shell? Escavalier has a great design! He has the knights helmet with a jutting steel jaw, and he has two jousts for arms; underneath it all, you can still see the Karrablast-like face. I also love the red stripes along the lances. This was by far the easiest poll for B/W!
I chose....Escavalier!