I agree with the mayority, either 1 or 4.
1 would be more contaned and personal, plus you can make the Lord Paramount an NPC and suddenly its all about the plotting, court intrigue and backstabing. I think in this case the Vale, Dorne the North or the Iron Isles would be the best choices as they are the most isolated (beffiting the game's contained nature).
4 Could be very interesting if properly managed (ie: no OP dragons) and as it has been said, the further away from canonical materials the better. For inspiration there was a very good game that I followed (didn't play) based of Viserys II and Aegon IV's reigns, lots of intrige, some war and the ocasional batshit-insane move (ah! King Hugo...).
