Not sure for favourite, but I really liked Gurren Lagann's artstyle. It wasn't the typical anime stuff. Everything was moving on screen in high speeds. Yet I could always tell what is going on. And a huge range of colors were used.
I also enjoy the infamous style of Jojo for it's distictiveness and how iconic it is. Yet as it is a manga adaptation, there are many still images with characters just posing and talking. Good show, but awful for an animation standpoint. Sadly this is true to many animes.
If you watch with subscribes it is not that evident because you are busy reading. But if you are watching dubbed, it is clear how most of the shows are just characters standing around doing nothing with zero coreography.
I know it is not comparable, but just watch the cutscenes made by Rockstar games. In most of their games there is always something happening in each cutscene. Characters move around, use their enviroments, show their emotions trough their body language. While in most animes, they just stand around and occassionally make "faces". Sure they are mostly well drawn. But boring af to look at.