I don't have a least favorite main character, since I enjoy all of them. However, if I really had to choose, Mr. Krabs would probably be last. He is still a good character though, although he is unlikeable in some episodes (especially the S6-8) episodes.
Least favorite character generally: Gary and Pearl (Both have grown on me a little, but I still usually find them the least interesting out of the main cast) Least favorite character in bad episodes: Even though he's one of my favorites usually, SpongeBob is absolutely unbearable whenever the plot forces him to be way too dumb or stalk and harrass Squidward.
Honestly idk if I have any least favorite characters. I used to say Pearl, but I don't really dislike her...I guess I just like her the least, I wish they did more with her or something. Maybe Patrick too, I just don't find him as funny as I used to.
Pearl, at the beginning. However, she's not as annoying as Mr. Krabs' thirst for money being more annoying than ever because he doesn't really have a soul/heart anymore. He literally just thinks about money and it didn't used to be like that.
Between Mr. Krabs and Patrick I think are my choices. Patrick is just stupidly annoying with how dumb he has become in the last 5-6 seasons. I just can't fathom how he became like this or WHY...