Ribbot is my favorite Jock villager, no contest. I've loved his design since seeing it in the player's guide for the GameCube game. Never had him as a villager back then, but eventually adopted him in one of my New Leaf towns alongside Sprocket and Del (well, I still need to scan Sprocket's amiibo in, but you get the idea). They have their own little corner of that town just for them and their cool robot business. I love his bolted together appearance, his headlight eyes, and the 59 painted on the back of his head. Oh, and the fact that since he's a Frog, he wouldn't use an umbrella when it rained in New Leaf. It's fun to give him robotic greetings and catchphrases too. I don't know why he's not more popular, he's probably my absolute favorite villager in the series.
My second vote on the poll would probably have to go to Sprocket. This a bit of a tough choice, but he has just enough to pull him into second place. He's not fully robotic in appearance like Ribbot is, with only his head and the tips of his wing and tailfeathers appearing mechanical and metallic, but that makes him unique unto himself as well. He's more like a cyborg. That's awesome. The same stuff about the dialogue applies to him too, of course. It also doesn't hurt that he's an Ostrich, one of my favorite species in Animal Crossing.
He doesn't get a vote on the poll, but third place is definitely Sterling. He gave Sprocket a run for his money because I love knight aesthetics in general and am fond of Knox and Sterling because of it. He and Knox are in my all-bird species New Leaf town, acting as the guards alongside Copper. Just wonderful.
Honorable mentions go to Boone, Bud, Cobb, Drift, Louie and Mott. Boone has that cool mandrill design, Bud's a fun surfer dude that's perfect for a New Horizon island, Cobb had that mad scientist thing going on in New Leaf and his green skin and yellow eyes make him look like a zombie (perhaps mad science gone awry?) or something, which I think is neat. Drift was, for a time, the mascot of my main (horror-themed) New Leaf town because his coloration includes Halloween's traditional colors of orange and black. Gotta love Louie's Donkey Kong design; I've never had him as a resident but have always wanted him in a town. Finally, Mott's just a good boy and is the obligatory lion star of my hybrid circus/magic show New Leaf town.