I feel the main storyline is longer, and more enjoyable on Oblivion, while the Skyrim main storyline just kind of... You know, ends? The story isn't very long in Skyrim either, can be completed in a couple of hours if you put your mind to it and know where to go.
As for the side quests and guilds. Oblivion had the Fighters Guild, which is essentially the Companions. However I feel that Skyrim most certainly wins on the sideline story and guilds. For example, the Companions storyline, to me, was more fun than the main quest line. The Thieves guild also, I am yet to do the Dark Brotherhood and the Civil War.
As for the side quests and guilds. Oblivion had the Fighters Guild, which is essentially the Companions. However I feel that Skyrim most certainly wins on the sideline story and guilds. For example, the Companions storyline, to me, was more fun than the main quest line. The Thieves guild also, I am yet to do the Dark Brotherhood and the Civil War.