Short answer: Two (sort of). Acadian, then Buffy.
Long answer: I started Oblivion in the summer of 2007. In typical fashion (for me), I created Acadian as a jack of all trades to evaluate the game and assess whether it was fit for elven consumption. Being a new game, I rebuilt Acadian numerous times as I learned more of the game. Indeed, he played variously as a Nord, Redguard and Breton as he grimly set about both the heroic and disgusting tasks required to explore every aspect of the game from Champion to Madgod to master of guilds and more. When, after more than a year of play and digesting UESP wiki and asking dumb questions on the BethSoft forum, we pretty much learned to optimize what the vanilla game of Oblivion could provide. It became time to transition Buffy the Bowranger from Baldur’s Gate II, and Buffy the Bowazon from Diablo II into Oblivion. Our first attempt or two were failures, so we spent a couple weeks time pondering things. On April 19, 2009, we tried again and successfully birthed Buffy the Bowgirl.
After 500 hours vanilla, we added a few mods, including a light in-game makeover, and continued her game up to 1000 hours. At that point, computer problems forced us to restart her. We took advantage of how much mods had advanced and used the opportunity to give her a pretty extensive makeover in the process, rebirthing her in January 2012. Since then, she has happily played daily to add 1900 additional hours to her previous game’s 1000.
Buffy completely drives the show on when/if we do quests and there are more that she will wrinkle her nose at than accept. This is fine since, thanks to the extensive groundwork slogged through by Acadian, my own curiosity about quests that don't suit her does not influence her choices. She quite simply never ever tires of visiting friends and guildmates all over Tamriel, traveling by horse and clearing dungeons. Fortunately, those things, and the activities that support them, never ‘run out’ in Oblivion. Her's is definitely a life of '
the journey is more important than the destination'.