Volcarona and Ferrothorn. Volcarona's like the strongest Bug-type with Quiver Dance and dangerous attacks with a high Sp. Atk, Sp. Def, and Speed. I raised one and it killed a Milotic with 4 QDs w/ Bug Buzz without dying when they were at the same level.
Ferrothorn is too defensive and strong with Curse, Gyro Ball, Earthquake, and Power Whip.