Who do you chose as medieval advisor? Edward Longshanks vs. Tywin Lannister

Tywin. So long as I don't go nuts, I think he would give me sound advice on how to keep the kingdoms peaceful.

Tywin

Of those choices, obviously Edward. Game of Thrones isn't based on any realistic time period in human history so any advice he had to give would be pretty useless.

And I'd also like to point out as a public notification, the Middle Ages were much much much less violent than how they're portrayed in modern media. It isn't really till the 1500s that the fricked up shite starts happening.

And for his time FWIW, Edward was considered one of the great British monarchs and a key figure in developing parliament and a constitutional government

Tywin, Longshanks was too arrogant and lacked the proper level of healthy respect for his enemies.

Tywin's only mistake was underestimating Tyrion.