From Smartest to Idiodic...
Plankton is the Smartest out of the 14 main characters in Spongebob Season 11. He is ranked as Superior.
Sandy is very, very, smart but not as smart as Plankton. She is Ranked as Genius
Bertha has a Bachlors degree in Oceanography and her family lives underwater so she can study Life in the Ocean. She is ranked as Smart.
Bartholemew is Blobby's pet Green Jellyfish. He is very tricky and mischievious and loves to pull pranks on imbecil characters. He is ranked as Mischievious
Lucian is Bertha and Aaron's Youngest Son. He is very good at Oceanography just likke his mother.