Cacturne...rockz!
Cacturne. Being Dark means to look sinister and scare off your opponents, which means Cacturne has it if you really look at him, especially the eyes and scarecrow shape 0.o
I used both of them in battle, but I'd rather go with power than speed. Shiftry has the speed and high hp to cover for the lower defense, but Cacturne has a higher attack and has a good movepool that has to do with status, which I am good to wield.
In the end, I love Cacturne, my 7th favorite Pokemon.