Smart, Tough Joffrey? A Euron Greyjoy POV? Check out "Dancing Stags"
Here's another Song of Ice and Fire alternate-universe treat from the alternate-history forum. It's entitled "Dancing Stags," available on fanfiction.net and on A03. The divergence (at least what I figure so far) is that Joffrey "Baratheon" (whose parentage might be a bit more complicated than in canon, since he's Lannister-blonde but has blue eyes) is born a bit earlier and gets some better parental attention. He's still not totally right in the head, but he's a lot smarter and physically tougher than in canon. There's an unfinished fan-fic in which the mind of Octavian from the HBO series Rome gets put in Joffrey's body and this portrayal of smart-Joffrey reminded of that, although Octavian in the show avoided doing violence himself if he could and Joffrey in this story is clearly well-trained for war.
The story begins with Joffrey learning of the death of Jon Arryn and coming up with some ideas of his own on who should be the new Warden of the East, ideas that don't really match up with his unpleasant mother Cersei Lannister's. He's got Waymar Royce as his buddy and henchman and is soon seeking to expand his influence farther in the Red Keep. From the way the story is told so far, we're going to have POVs from Jon Snow, Renly Baratheon, Balon Greyjoy, and (drumroll please) Euron Greyjoy.
Euron is an interesting character. He's an out-and-out monster with a thing for grand over-dramatic gestures, ironic punishments for his enemies (cutting an Ironborn who had adopted the Faith of the Seven into seven pieces, for example), and playing mind games with even his own family members, but he's got a serious Evil Is Cool thing going. It's ultimately revealed that he practices sorcerery and is intent on marrying Danaerys Targaryen and using a supernatural horn to take control of her dragons so the Ironborn can conquer Westeros. I find the character of Euron so interesting I actually came up with an "Euron Greyjoy with the serial numbers filed off" character for a fantasy trilogy who starts out in a fantasyland version of the Kingdom of the Isles and ends up in the fantasyland version of Morocco in his quest to tame dragons. There's some stuff from Norse mythology thrown in there too--hint: It involves just how and why Odin lost his eye. I've got a friend who's into Villain Protagonists, so he might like this one.
In any event, other than the story with Octavian-in-Joffrey, I have never seen a story where Joffrey is anything but a worthless little piece of garbage, let alone an evil mastermind in his own right. This could go some very interesting places...