I can't really talk since I've only played Skyrim (playing right now actually)

Oblivion has story and mechanics, Skyrim has the other stuff. I split the dif and play Fallout.

Morrowind hands down. Oblivion and Skyrim don't even come close.

Morrowind, its really immersive once you get into it

I like Morrowind because it has the most variety in terms of gameplay and is complex enough to be fun. The story and lore are amazing and very unique. Spears. It offers more opportunities for role-playing. And is very nonlinear (compared to Skyrim or Oblivion).

Definitely oblivion. Among a lot of other reasons, the one that takes the cake is because of Martin Septum lol

Morrowind feels like the best elder scrolls because of the uniquely alien landscape. The ashy valleys and mushroom forests. The archipelago of unconnected islands all around and the many different spells and effects. The quests left you to really pay attention and figure it out and the limited fast travel system really made you think about how to get where you needed to go. The “travel” spells were super fun and handy. Levitation, mark and recall, hoptoad, fast swim, water breathing, water walking, slow fall. And even Almsivi intervention and divine intervention where cool, If you remembered where temples where. It feels when I play it even now to be a very detailed game. Even after 20 years.