I love Get Schwifty with the giant heads - just a weird episode. I also like Mr. Methinks episode. Very dark. I like all of them when they are more inter dimensional.
Tough call. Mr. Meeseeks was the first one that came to mind but the Total Rickall where they all have false memories of extra family members is so good. No wrong answers here, except maybe for the metaplot ones about the Morty takeover of the Citadel.
I like the "Tiny Rick" one where Rick goes back to High School. The scene where Summer and Morty force Tiny Rick to listen to Elliott Smith cracks me up. It doesn't hurt that I'm a big Elliott Smith fan. The interdimensional cable one is pretty funny too. I need to get a shirt with "Ball Fondlers" on it.