License to Milkshake is a top 20 SB episode of all-time. The concept, the jokes, the storyline, the plot all work here.
Gullible Pants is critically underrated in my opinion. I laughed out loud throughout the 2nd half of the episode, not to mention the first half was funny as well. My favorite line is: "Squidward sleeping on the job?" "Okay, that's actually normal". (even typing this out is giving me a good laugh). I'd rank this top 10-15 in SpongeBob history, as well as the best in Season 6 by far.
Choir Boys, The Splinter, Boating Buddies, To Love a Patty, Waiting, Good Neighbors, and What Ever Happened to SpongeBob are episodes people really do not like I enjoy in some capacity.
Shell Shocked, Hello Bikini Bottom, and The Abrasive Side are episodes people like that I do not enjoy.