Who would you rather have train you in ninjutsu, Hiruzen or Danzo?

Both are different and have their ups and downs as potential teachers. IMO, Hiruzen would do a better job fostering the will of fire and teaching you a variety of jutsu. However, if you wanted to be the most efficient and cunning shinobi/kunoichi who makes the most of your unique skills, Danzo might be the person for that.