Squidward's best season is Season 3. The play off between him towards SpongeBob and Patrick is just awesome. Episodes like Idiot Box, Just One Bite, Snowball Effect, and The Camping Episode, all show his character almost beautifully. He doesn't want to like their games, but he can get carried into it. The best Squidward episode, however, comes from Season 2. Squidville shows his character to the tee. He needs SpongeBob to fulfill an otherwise boring life. Squidward and SpongeBob is the best duo on the show, with episodes like Pizza Delivery, Employee of the Month, Dying For Pie, Graveyard Shift, and Just One Bite. I love the dynamic between Squidward's more pessimist attitude with SpongeBob. He can be a great straight-man and can be very relatable in these moments. Then there is the episode Can You Spare a Dime? where it shows Squidward is completely capable of taking advantage of SpongeBob. He had a certain edge to him that didn't make him all the way in one direction, which I really like, he deserved his treatment in that episode.
Squidward on his own is a great character as well. His motivations make sense, he doesn't want to harm SpongeBob he just wants for him to leave him alone. He wants everyone to shut up and to relax by himself. That is why he always has a bad mood when he's at work. An episode the captivated his interests is Band Geeks and Squilliam Returns. They show that he really does have something to live up to towards his rival, and Band Geeks really does get down exactly his personality. Squilliam Returns serves as a great sequel showing that Squidward can lose in the feud.
Nowadays, he's ether a punching bag or way too out of mood. He doesn't really feel like Squidward anymore. Episodes like Squid Noir are cool and all, but it feels like a different Squidward doing it. It doesn't really feel like the same person, it's kind of hard to put my hand on it, but it is odd. He's probably, excluding Plankton, the least effected by flanderization, since being a punching bag doesn't make you unlikable. An episode that kills his personality the most is Little Yellow Book, showing him being unlikable with no real follow through, making the whole experience suck.