Drop everything, train a full team of Leavanny. ROFL at your opponents confusion and wear straightjacket.
Actually on topic though a leavanny is a solid choice for any team. Grass/Bug typing gives it some solid coverage and its got two very nice STABs in the form of X-Scissor and Leaf Blade. Heres what i would suggest for a setup.
This set-up gives Leavanny excellent coverage and utility. Hone Claws gives a +1 to Attack and Accuracy, allowing it to boost through annoying double teams, sand attacks, or any accuarcy lowering/evasion raising move. Swords Dance allows it to get a solid +2 to Attack, making its two STABs to hit that much harder.
Leavanny about to faint? no worries, Baton Pass the boosts to another pokemon that can take advantage of them. Shes squishy though, Fire-type damage hits for a whopping 4x damage, same for Flying-type attacks. Her grass typing gives her a weakness to her secondary typing. Rock hits for 2x and so does poison.
Theres her total stat spread, with min/max for those interested. Shes got decent speed, allowing her to outpace some major threats to her, allowing for either a swords dance/baton pass combo or a couple of hits in. Shes got a lot of options available to her, with the one i listed being a really good one if she can sponge the hits to get a setup.