It doesn't make any sense to me that Shelmet evolves into Accelgor and Karrablast evolves into Escavalier; I understand that there is a Karrablast inside the Escavalier, but Shelmet is such an obvious predecessor to him.
I think it would be more appropriate if Shelmet + Karrablast evolved into Escavalier and Accelgor was a stand alone Pokemon, but obviously, such things do not exist within the rules of Pokemon (except in the case of Regigigas using special rules).
At first I liked Accelgor more, but then Escavalier grew on me, but ultimately I had to acknowledge that I like Accelgor more by far.
Obviously he serves a sort of specialty purpose, who is best used wasting other Pokemon's high speed scores by having a higher speed score; with only four bug type moves though, most of them weak or physical, his bug type is wasted, without other special bug type moves like Signal Beam or Silver Wind.
I think the design on both of them is pretty poor, for example, Escavalier is full of flinch moves, which only really makes sense in a Trick Room set-up, which is an ability that he doesn't possess; the gameplay is just too cheeky for me to admire.