Ferrothorn. It has a great defensive movepool in Leech Seed, Stealth Rock, Spikes, Thunderwave and more. It has awesome defenses and typing with just 2 weaknesses. Also it's base 94 attack is pretty decent and with a few good offensive moves in Gyro Ball and Power Whip it can put a hole in many teams. It is very good at putting up hazards and/or stalling with Leech Seed and Leftovers. I have been annoyed by the Leech Seed + Leftovers + Protect combo and it is not fun to deal with :P
Hope I helped! :)
