I'm not entirely sure who my favorite Cranky villager is. It's a toss-up between Hopper, Octavian, and Rasher.
I've always been a fan of Hopper's design, and actually had him in my original town back on the GameCube game. I restarted that town pretty quickly, unfortunately, and never managed to reclaim him until I decided to create an all-bird town in New Leaf. Penguins are among my favorite animals, his demeanor is great, and his design is unique. He's an overall great villager.
I originally encountered Octavian back on the GameCube game when playing with a friend in their town. I thought he was really cool since, at the time, he was the only octopus villager. He actually moved out of my friend's town and into mine (which my friend wasn't all too happy about) and remained there for a little while, but eventually moved out too. I reclaimed him in New Leaf years later and he has been in my town ever since. I still like him the most of all of three of the octopus villagers.
As for Rasher, his design just gives off so much character. His scars make him look pretty neat, and the way he grins is great.
I'm also a fan of Apollo, Avery, Bruce, Butch, Camofrog, Del, Frank, Gruff, Knox, and Walt. As you can probably tell, Cranky is one of my favorite personality types overall.