Oblivion. It was just sooo much more memorable to me! I have a ton of great memories playing Oblivion, and very few playing Skyrim. Skyrim is just... bland. It's snow snow snow everywhere, and the music is... forgetable honestly... Here, let me put two random tracks from each game side by side.
[video=youtube;ez7SL6-HyGA]http://www.youtube.com/watch?v=ez7SL6-HyGA[/video]
[video=youtube;9OGGggY6pAo]http://www.youtube.com/watch?v=9OGGggY6pAo[/video]
I don't know what it is, I just prefer Oblivion's music so much more. Like, Skyrim's music sounds good when you're listening to it, but you can't really hum it again later. Like I said - forgetable IMO.
I also thought the story was infinitely better in Oblivion. The Emperor has been killed, oh no! The Gray Fox, is he really just a legend? Who's the traitor in the Dark Brotherhood?! In Skyrim, aside from the main quest (which I'll admit was pretty good), the stories behind the Mage's Guild, Thieve's Guild, and Dark Brotherhood all sucked. I found TES IV way more immersive.
But I'll give Skyrim credit, the combat was a lot better than Oblivion's. However, I don't play an RPG for the combat. I may be a minority here, but I just really like stories and feeling apart of the world. And you may say Skyrim's graphics made you feel apart of the world, but honestly, I don't even give Skyrim the edge in terms of looks. It's bland. Boring. Oblivion's lushious greenery combined with its upbeat score is way more preferable.
And to be honest, I like getting in trouble with the law and having an Oblivion guard pop out of nowhere and say, "STOP! YOU VIOLATED THE LAW!" It's corny and reminds me why I cherished Oblivion so.