Wow, that's a rather hard decision for me, cause I am not such a big fan of any of them, probably also because I did not have that much of them.
I probably go with Camofrog, because for a cranky, he was quite easy to befriend and was never too unfriendly. Also, I like his design.
Gigi on the other hand... hate her with a burning passion.
Lily, I think. I had Diva for so long in a spot I wanted to develop just refusing to move out. She kind of put me off having frogs in my town. Thanks, Diva.
For me, Ribbot. I'm not a fan of his Jock personality, but I really like his interior and his appearance. Really cool. I think Wart Jr. is also a favorite - he's just awfully cute!
My favorite frog villager is Ribbot, by a wide margin. I love the robot design and hope we receive more robot villagers in the future.
I like a few other frogs as well. Honorable mentions go to Camofrog, Diva, Drift, and Gigi. I really like the idea behind Raddle, love the surgical mask, the furniture he offers from his RV, and the interior design of his home, but I find his overall design lacking; his eyes, compared to everything else, don't look good and kind of ruin the otherwise great design. I've had Lily as a resident in one of my towns and she's nice, but not one of my favorites. I grew to like Jambette after not liking her at first, but she's also not a favorite either.
Raddle is one of my favorite villagers period. I love the poison dart frog design with his mask and creepy doctor vibe, the fact that he is a lazy villager(one of my favorite personality types), and his creepy white-out eyes that go pink when he is startled.
I can't pick only one frog villager.
Puddles and Frobert are my least favourite villagers. Every frog else I'm okay with. I really love Lily, though. She lives in my town.