According to a character poll conducted, the most popular character is Haibara Ai.
there isen't really one most popular character i think the most popular would be Suigintou, Suiseseki, Hina Ichigo and Shinku.
Vegeta or gokuits character and its goku
The most popular character in Final Fantasy XIII (13) is Lightning. She is the main protagonist and is on the cover of the case.
darth vader
Togera
shikamaru
toon link
konohomaru
Snooki
susan
There really isn't anyway togaugewho is the most popular, but it could be Roger.