Both games would be deeper than what your friends might be used to, but I'd say that Game of Thrones will be more accessible than Warrior Knights. Either game will take about three to four hours for an average game, but Game of Thrones is more streamlined in some key ways; there aren't as many different things happening on-board with different ways to resolve them, so it's easier to keep straight.
Have your friends ever played Diplomacy? If so, they'll have a good foundation for picking up Game of Thrones.
(I have both games and enjoy both. I know that I don't get a chance to play Warrior Knights as often, because it is a bit more complex of a game. Also, Game of Thrones has the licensing hook, and for some people, that's enough to keep them coming back.)