While personally I like Leavanny more, I must disagree with PikachuSwagg. Unless you have Sun support and are running Chloropyll Scolipede is much better.
His high speed and good movepool, combined with Swords-dance to boost Attack makes him an amazing sweeper. He can also set up spikes and Toxic spikes, and even Baton pass. He is a very diverse and powerful Pokemon. He also is the fastest Pokemon (aside from Chlorophyll boosted Sawsbuck) with Megahorn. This guy strikes fear into the hearts of RU Dark, Grass, and Psychic types. Furthermore it has less weaknesses than Leavanny and no double weaknesses. Choose Scolipede.