I find it a close tie betwen Gen 3 (Ground/Water, Fire/Fighting Decent assault Grass line) vs. (Water/Steel, Fire/fighting [although Infernape was more used, with exception to Speed Boost] and Grass/Ground.) --- Ignoring sheep. Best solution on CoD boards.
For me this is easily Gen 4, all three were awesome.
A steel emperor penguin is just about the coolest thing you could ever imagine, a fire/fighting monkey that is like Blaziken but better (I'm going to ignore Speed Boost because I can't access it ) and of course you can never, ever go wrong with turtles, especially when they are creative and don't just make it a water type. It's a no brainer.