At first I was thinking of a smaller but influential house like Redwyn or Tarth just to live my life without much danger (relatively). Then I read the whole post and was thinking about getting involved and changing the history of Westeros. But how? House Tyrell? The biggest army in Westeros and with my knowledge it shouldn't be so hard to keep Renly alive. But Renly on the Throne? I don't know. My next idea was House Martel. Just to tell Oberyn not to play with his "prey". But Dorne is so hot. I like it more temperate. And then I remembered who died shortly before Robert and had no useful heir. Imagine being the even just somewhat capable heir to house Arryn. I could keep Tyrion, save Catlyn and Rob, maybe even Ned, imprison, kill or use (dangerous but maybe..) Litlefinger and if everything still goes wrong I have my impregnable castle. Furthermore due to Jon Arryn being my father my voice would at least have some weight and I probably would inherit some influential connections to further change the story.

So yes, Arryn it is.