I love The Elder Scrolls so much, but I can never express my love for the series in words. Maybe if I wrote a 10,000 words essay. Maybe I'll do that someday.
While I think Morrowind is the best one, Skyrim has a special place in my heart for being the one that really got me into the series. My brother played Oblivion a lot back in 2012, but sold it before I got the time to play it. I got Skyrim not too long ago, and it didn't take long until I became competely addicted. It only got worse from there. While I like Oblivion a lot too, it's lacking in some areas I think Skyrim peformed better in. Like having interesting lore, varied environments (I blame Talos), a lot of things to do, better (but still not good) combat, more varied voice acting and a much better leveling system.
So, in the end I'd say Skyrim is my favourite. I'm such a casual.