Bigbaby
conquering the north is the same as taking on all of westeros. the sansa option seems the most feasable. also if she is engaged to ragnar prior to the king coming to winterfell to make ned the hand. she will never have to go to kings landing and then you can have her be queen of the north during the war after ned dies. or you can use this to save him. but if she becomes queen ragnar will become king when they are wed.